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Metal-containing clusters and complexes may represent active sites in heterogeneous catalysts, where catalytic transformations take place, thus offering an elegant approach in studying the fundamental interactions in a simplified way. In this thesis, infrared-(multiple) photodissociation spectroscopy is used to study metal-containing clusters and complexes with atmospherically relevant adsorbates to learn about their reactivity, structural binding motifs, and the degree of activation of adsorbed moieties. Complementary density functional theory calculations help in the assignment of experimentally observed phenomena. Each chapter describes a different system that presents unique and sometimes unexpected results. N2O binding to Pt+n proves to be size-dependent; small clusters form molecular N2O adsorption products whereas larger ones react to produce PtO+, and similar chemistry is observed upon infrared excitation. Examining N2O binding to Au+n and Co+n reveals inertness of gold clusters whereas cobalt species prove to be similar in their reactivity to platinum. Size-selective cooperative binding effects are discovered for AunO2CO− species both from mass spectrometry and spectroscopy. Infrared action spectra of Co(NO)+n and Rh(NO)+n complexes disclose spectral differences in the number and position of the bands as well as similarities in the NO binding motifs to these metal centres. Rh(CO)n(N2O)+m system proves to be different than Au(CO)n(N2O)+m studied by the Mackenzie group previously, and these observations are explained in terms of different electronic structures, relative binding energies, and coordination numbers. Isotopic study of Au(CO)n(N2O)+m using 13CO reveals a band in the infrared spectrum of the Au(12CO)2(N2O)+ complex that is an overlap between individual 12C≡O and N2O N=N vibrational bands.

This paper reports on the characterization of the stereo-dynamic controlling three different chemi-ionization reactions, recent objective of our study, since they participate to the balance of phenomena occurring in plasma, interstellar medium, planetary atmospheres, flames and lasers. The optical potential, obtained by a phenomenological method and defined in the whole space of the relative configurations of reagents, has been formulated in an accurate and internally consistent way for three different systems. Some cuts of the multidimensional potential, that asymptotically correlate with a specific fine level of the open shell atom and/or with a defined orientation of the molecular reagent, have been exploited in the present study to emphasize crucial features of the collision dynamics along selected entrance channels of the reactions. Consistently, basic quantities determining the topology of the reaction stereo-dynamics have been properly defined, emphasizing in the three cases relevant changes in the microscopic reaction evolution. Much attention focused on the selectivity of the orbital angular momentum, affecting each collision event at any chosen collision energy. It controls the relative weight of two different reaction mechanisms. The direct reaction mechanism is driven by short-range chemical forces, promoting, by direct electron transfer between reagents, a prototypical elementary oxidation reaction. The indirect mechanism, controlled by the combination of long-range chemical and physical forces, can be triggered by a virtual photon exchanged between reagents, promoting a sort of photo-ionization process. Obtained results and emphasized differences appear to be of general interest for many other elementary processes, more difficult to characterize at this level of detail. Graphic abstract

The reaction of excited nitrogen atoms N(2D) with CH3CCH (methylacetylene) was investigated under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy (Ec) of 31.0 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction micromechanism. Theoretically, the reaction is found to proceed via a barrierless addition of N(2D) to the carbon–carbon triple bond of CH3CCH and an insertion of N(2D) into the CH bond of the methyl group, followed by the formation of cyclic and linear intermediates that can undergo H, CH3, and C2H elimination or isomerize to other intermediates before unimolecularly decaying to a variety of products. Kinetic calculations for addition and insertion mechanisms and statistical (Rice-Ramsperger-Kassel-Marcus) computations of product branching fractions (BFs) on the theoretical PES were performed at different values of total energy, including the one corresponding to the temperature (175 K) of Titan’s stratosphere and that of the CMB experiment. Up to 14 competing product channels were statistically predicted, with the main ones, at Ec = 31.0 kJ/mol, being the formation of CH2NH (methanimine) + C2H (ethylidyne) (BF = 0.41), c-C(N)CH + CH3 (BF = 0.32), CH2CHCN (acrylonitrile) + H (BF = 0.12), and c-CH2C(N)CH + H (BF = 0.04). Of the 14 possible channels, seven correspond to H displacement channels of different exothermicity, for a total H channel BF of ∼0.25 at Ec = 31.0 kJ/mol. Experimentally, dynamical information could only be obtained about the overall H channels. In particular, the experiment corroborates the formation of acrylonitrile + H, which is the most exothermic of all 14 reaction channels and is theoretically calculated to be the dominant H-forming channel (BF = 0.12). The products containing a novel C–N bond could be potential precursors to form other nitriles (C2N2, C3N) or more complex organic species containing N atoms in planetary atmospheres, such as those of Titan and Pluto. Overall, the results are expected to have a potentially significant impact on the understanding of the gas-phase chemistry of Titan’s atmosphere and the modeling of that atmosphere.

Ionization cross sections for Ne*(3P2,0)–HX (X = Cl, Br) chemi-ionizations are presented in the 0.02–0.5 eV collision energy range.

Nanoporous gold (np-Au) is a pure metal-based catalyst, which forms methyl formate very selectively in the partial oxidation of methanol. Although several model studies under ultrahigh vacuum as well as quantum mechanical calculations attempted to provide insight into the structural and catalytic properties of np-Au, the understanding of the factors leading to the high activity and selectivity remain incomplete. In this work, a single crystalline Au(332) surface was used to model structural properties like low index (111) facets as well as low coordinated Au atoms. The experiments were conducted under well-defined UHV conditions by pulsed, isothermal molecular beam (MB) experiments combined with in situ infrared reflection adsorption spectroscopy (IRAS) as well as temperature programmed reaction (TPR) experiments. Using CO as a probe molecule applying isotopically diluted gas mixtures to prevent dipolar coupling between CO molecules, the several adsorption sites on Au(332) were spectroscopically evidenced and assigned by a combination with DFT calculations. In isothermal MB experiments on the partial methanol oxidation to methyl formate, varying the surface temperature as well as the methanol and oxygen fluxes revealed two distinct surface deactivation processes for methyl formate formation due to the formation of formate and due to impurities in the used methanol. Low coordinated sites were found to form methyl formate at a higher rate compared to other sites on the Au(332), while other reaction steps, e.g. formation of methoxy proceed also effectively on terrace sites and with gold-oxygen (AuOx) phases. TPR results demonstrated unwanted oxidation of methyl formate, the desired partial oxidation product in methanol oxidation, to occur on Au(332) already at low temperatures and even for low oxygen coverages, as expected for typical reaction conditions on np-Au. Three different reaction mechanisms for CO2 formation from methyl formate were identified by isotopic labeling experiments, which were connected to specific oxygen species on minority sites. Due to its dependence on oxygen at special sites, the methyl formate oxidation is slow under isothermal conditions compared to the oxidation of methanol which provides a microscopic understanding of the high selectivity of np-Au on the formation of methyl formate.

This chapter discusses three examples of quantum effects that can be observed in state-of-the-art experiments with molecular beams—scattering resonances as a probe of interparticle interactions in cold collisions, the protection of Fano-Feshbach resonances against decay despite resonant coupling to a scattering continuum, and a circular dichroism in photoelectron angular distributions arising in the photoionization of randomly oriented chiral molecules. The molecular beam setup provides molecules in well-defined quantum states. This, together with a theoretical description based on first principles, allows for excellent agreement between theoretical prediction and experimental observation and thus a rigorous understanding of the observed quantum effects.

The aim of this thesis is to investigate the effects of change in the chain length and chlorine group position on C-Cl bond photodissociation dynamics of chloroalkanes using the velocity map imaging (VMI) method. Three different chloroalkanes are studied (1-chloropropane, 2-chloropropane, 1-chloropentane) and compared with previously investigated chloromethane. Regardless of the parent chloroalkane, measured kinetic energy distributions (KEDs) of chlorine photofragments exhibit a single peak at energy around 0.8 eV. Photodissociation of higher chloroalkanes involves a recoil of a semi-rigid alkyl fragment, whose internal energy absorbs 40-60% of the total available energy. For chloromethane, however, only less than 10% of the available energy goes into the alkyl fragment excitation. Measured results of the energy partitioning are compared with cal- culations based on classical impulsive models. VMI experiment in combination with theory also yields information about the nature of electronic transition and probability of the intersystem crossing. Analysis indicates that the direct absorp- tion into the triplet state is more probable for the chloroalkanes with longer chain length, especially for the branched one. 1

In the common perception of catalysis, a catalyst should typically possess multiple functionalities in order to promote several individual reactions within a multi-step process. A promising way to approach this concept relies on functionalization of a catalytic surface with organic ligands, e.g. organic adsorbate or covalently bonded functional groups, to allow for a selective and controlled promotion of the desired reaction path via lateral reactant-ligand interactions. In such functionalized systems, the role of ligands can be multifold: it can either impose a geometrical constraint on the surface, hence affecting the interaction of the adsorbates with the underlying metal substrate, and/or undergo more specific intermolecular interaction, as in building a 1:1 complex with the reactant that affects its electronic structure or adsorption geometry. Despite ongoing vigorous progress in this field, the development of powdered heterogeneous catalysts of practical relevance, frequently relies on trial and error. For establishing a more rational approach towards synthesis of new advanced functionalized catalytic materials, the atomistic-level understanding of the mechanisms governing ligand-directed heterogeneous catalysis has to be significantly improved. Towards this goal, a new experimental setup was designed and built which allows us to prepare and characterize ligand-modified model catalysts under well-controlled UHV conditions and investigate reactive surface processes across a broad pressure regime, from UHV and up to the near ambient. Integrative measuring techniques, capable of probing the mechanisms, kinetics and dynamics of such processes, namely molecular beams and infrared reflection absorption spectroscopy, were installed and applied in this work. Two case studies were performed by the newly built setup, aiming at exploring the lateral interactions between adsorbates on Pt(111) surface. Complementary, scanning tunneling microscopy was employed to obtain real space information on the distribution of the adsorbates. First, we show that a lateral interaction, mediated by hydrogen bonding between two adjacent acetophenone molecules, triggers the formation and stabilization of the normally unstable enol tautomer of acetophenone. This interaction is a crucial first step in the hydrogenation of the molecule. More importantly, we also provide a strong experimental evidence that confirms theoretical predictions that transformation of simple carbonyl compounds to their enol part enables low-barrier hydrogenation pathway of normally very stable C=O compounds. The second case reported in this dissertation involves a chiral modification of the surface with (R)-(+)-1-(1-naphthylethylamine) (R-NEA) and its interaction with CO that was utilized as a simple proxy for carbonyl compounds. The combination of spectroscopic and microscopic observations shows that the R-NEA molecules are self-assembled into directed short chains, clearly suggesting an intermolecular interaction between individual molecules. The individual molecules in the chains are also strongly inclined with respect to the surface plane as established spectroscopically. The adsorption geometry of R-NEA was found to be greatly affected by co-adsorption of CO, and the observed spectral changes induced in this process are indicative of a strong intermolecular interaction between CO and adsorbed R-NEA molecules, most likely the amino-group., Ein Katalysator sollte typischerweise mehrere Funktionalitäten besitzen, um mehrere Einzelreaktionen innerhalb eines mehrstufigen Prozesses spezifisch zu beschleunigen. Ein vielversprechender Ansatz beruht auf der Funktionalisierung einer katalytischen Oberfläche mit organischen Liganden. In solchen funktionalisierten Systemen kann die Rolle der Liganden vielfältig sein: Diese können entweder der Oberfläche eine geometrische Beschränkung auferlegen, wodurch die Wechselwirkung der Adsorbate mit dem darunter liegenden Metallsubstrat beeinflusst wird, und/oder diese können spezifische intermolekulare Wechselwirkungen eingehen, wie beim Aufbau eines 1:1-Komplexes mit dem Reaktanten, der die elektronische Struktur oder die Adsorptionsgeometrie beeinflusst. Trotz anhaltender Fortschritte auf diesem Gebiet beruht die Entwicklung pulverförmiger heterogener Katalysatoren von praktischer Relevanz häufig auf dem Prinzip des „Trial and Error“. Um einen rationaleren Ansatz für die Synthese neuer funktionalisierter Katalysatoren zu finden, muss das atomistische Verständnis der Mechanismen für die ligandendirigierte heterogene Katalyse verbessert werden. Zu diesem Zweck wurde ein neuer Versuchsaufbau verwirklicht, der es uns ermöglicht, ligandenmodifizierte Modellkatalysatoren unter kontrollierten UHV-Bedingungen herzustellen und zu charakterisieren und deren reaktive Oberflächenprozesse über einen breiten Druckbereich (10-10 – 1000 mbar) zu untersuchen. In dieser Arbeit wurden zur Aufklärung der Mechanismen, Kinetik und Dynamik Molekularstrahlexperimente und Infrarot-Reflexionsabsorptionsspektroskopie durchgeführt. Es wurden zwei Fallstudien durchgeführt, um die lateralen Wechselwirkungen zwischen Adsorbaten auf der Pt(111)-Oberfläche zu untersuchen. Komplementär zu den oben genannten Messtechniken wurde die Rastertunnelmikropskopie eingesetzt, um Informationen über die tatsächliche Verteilung der Adsorbate auf der Substratoberfläche zu erhalten. Es konnte gezeigt werden, dass die laterale Wechselwirkung, welche auf Wasserstoffbrückenbindungen zweier benachbarter Acetophenon-Moleküle beruht, die Bildung und Stabiliserung des normalerweisen instabilen Enoltautomers von Acetophenon auslöst. Diese beobachtete Wechselwirkung ist dabei ein entscheidender erster Schritt bei der Hydrierung des Moleküls. Darüber hinaus konnten aussagekräftige experimentelle Beweise geliefert werden, welche die theoretischen Vorhersagen bestätigen, dass die Umwandlung einfacher Carbonylverbindungen in das korrespondierende Enoltautomer einen energetisch günstigeren Reaktionspfad für die Hydrierung der normalerweise sehr stabilen C=O-Gruppe darstellt. Die Zweite in dieser Dissertation beschriebene Studie betrifft eine chirale Modifikation der Oberfläche mit (R)-(+)-1-(1-Naphthylethylamin) (R-NEA) und dessen Wechselwirkung mit CO, das als einfachster Vertreter von Carbonyl-Verbindungen verwendet wurde. Die Kombination von spektroskopischen und mikroskopischen Beobachtungen zeigen, dass sich die R-NEA-Moleküle in gerichteten kurzen Ketten selbstanordnen, was eindeutig auf eine intermolekulare Wechselwirkung zwischen einzelnen Molekülen hindeutet. Spektropskopisch kann gezeigt werden, dass die einzelnen Moleküle in diesen Ketten in Bezug auf die Oberfläche stark geneigt sind. Es wurde festgestellt, dass die Adsorptionsgeometrie von R-NEA durch die Ko-Adsorption von CO stark beeinflusst wird und die beobachteten spektralen Änderungen weisen auf eine starke intermolekulare Wechselwirkung zwischen CO und adsorbierten R-NEA-Molekülen hin, höchstwahrscheinlich der Aminogruppe.

Studies of neutral biomolecules in the gas phase allow for the study of molecular properties in the absence of solvent and charge effects, thus complementing spectroscopic and analytical methods in solution or in ion traps. Some properties, such as the static electronic susceptibility, are best accessed in experiments that act on the motion of the neutral molecules in an electric field. Here, we screen seven peptides for their thermal stability and electron impact ionizability. We identify two tripeptides as sufficiently volatile and thermostable to be evaporated and interfered in the long-baseline universal matter-wave interferometer. Monitoring the deflection of the interferometric molecular nanopattern in a tailored external electric field allows us to measure the static molecular susceptibility of Ala-Trp-Ala and Ala-Ala-Trp bearing fluorinated alkyl chains at C- and N-termini. The respective values are 4 π e 0 × 330 ± 150 A 3 and 4 π e 0 × 270 ± 80 A 3 .

In combustion, the overall chemical changeover is the result of an intricate network of elementary reactions (unimolecular, bimolecular and termolecular) which are classified according to their role (initiation, propagation, branching, termination steps) in the chain reaction. To implement a realistic combustion model, a deep knowledge of the chemical transformation at the molecular level for all the important steps is crucial. In this contribution, the capabilities of the crossed molecular beam (CMB) method with mass spectrometric (MS) detection in the study of multi-channel elementary reactions of relevance in combustion chemistry are illustrated by several examples of reactions involving atomic oxygen and C4 unsaturated hydrocarbons. In particular, the focus will be on the almost unique capability of the CMB-MS method in identifying the reactions products and their branching ratios by means of the same detection scheme and under well-controlled conditions. As expected, the initial steps of the reactions between atomic oxygen and C4 unsaturated hydrocarbons are similar to that of the other reactions that involve O and smaller unsaturated hydrocarbons, as they all feature the attack of the electrophilic O atom to the π density of the multiple bond(s). However, the much more complex molecular structure leads to an increase of the possible reaction channels. Intersystem crossing (ISC) from the triplet potential energy surface to the lower energy singlet one via intersystem crossing is significant and opens, also in this case, several reaction channels which are not otherwise available. Several pairs of products formed after ISC are closed-shell molecules, rather than open-shell radicals. Clearly, this observation has strong implications for combustion modeling, because ISC shifts part of the reactive flux toward terminating rather than propagation or branching steps.

The electrostatic hexapole is a versatile device that has been used for many years in gas-phase experiments. Its inhomogeneous electric field has been employed for many purposes such as the selection of rotational states, the selection of clusters, the focusing of molecular beams, and molecular alignment as a precursor for molecular orientation. In the last few years, the hexapolar electric field has been demonstrated to be able to control the conformer composition of molecular beams. The key point is that conformers, where the component of the permanent electric dipole moment with respect to the largest of the principal axes of inertia is close to zero, require more intense hexapolar electric fields to be focused with respect to the other conformers. Here, we simulated the focusing curves of the conformers of 1-chloroethanol and 2-chloroethanol under hypothetical beam conditions, identical for all conformers, in a hypothetical and realistic experimental setup with three different hexapole lengths: 0.5, 1, and 2 m. The objective was to characterize this selection process to set up collision experiments on conformer-selected beams that provide information on the van der Waals clusters formed in collision processes.

International audience; We present a brief review of our progress towards measuring parity violation in heavy-metal chiral complexes using mid-infrared Ramsey interferometry. We discuss our progress addressing the main challenges, including the development of buffer-gas sources of slow, cold polyatomic molecules, and the frequency-stabilisation of quantum cascade lasers calibrated using primary frequency standards. We report investigations on achiral test species of which promising chiral derivatives have been synthesized.

Title: Mass spectrometric and optical spectroscopy studies of clusters and nano- particles in molecular beams Author: Kamila Moriová Institue: Institute of Physics of Charles University Supervisor: doc. Mgr. Michal Fárník, Ph.D., DSc., J. Heyrovský Institute of Phy- sical Chemistry of the CAS Consultant: RNDr. Václav Profant, Ph.D., Institute of Physics of Charles Uni- versity Abstract: Condensation of ices on the surface of dust grains with activation of these ices by cosmic rays in interstellar medium can lead to formation of complex chemical species. In the present work we primarily examine ammonia clusters, which represent a model system of ice particles. Large ammonia clusters were prepared in molecular beams and pass through a pickup chamber in which me- thanol molecules were captured. After electron ionization of (NH3)N (CH3OH)M clusters, a mass spectrum of ionic fragments was obtained in which fragments with methanol (NH3)n(CH3OH)mH+ predominated over the pure ammonia frag- ments (NH3)nH+ : at least one methanol molecule was present in 75 % fragments. This is in disproportion with the composition of the original neutral precursors, which contain less than 4 % of methanol. Based on the measurement results, we suggest that ammonia is ionized in the first place resulting in the NH+ 4 ion core solvated...

STIRAP (stimulated Raman adiabatic passage) is a powerful laser-based method, usually involving two photons, for efficient and selective transfer of populations between quantum states. A particularly interesting feature is the fact that the coupling between the initial and the final quantum states is via an intermediate state, even though the lifetime of the latter can be much shorter than the interaction time with the laser radiation. Nevertheless, spontaneous emission from the intermediate state is prevented by quantum interference. Maintaining the coherence between the initial and final state throughout the transfer process is crucial. STIRAP was initially developed with applications in chemical dynamics in mind. That is why the original paper of 1990 was published in The Journal of Chemical Physics. However, from about the year 2000, the unique capabilities of STIRAP and its robustness with respect to small variations in some experimental parameters stimulated many researchers to apply the scheme to a variety of other fields of physics. The successes of these efforts are documented in this collection of articles. In Part A the experimental success of STIRAP in manipulating or controlling molecules, photons, ions or even quantum systems in a solid-state environment is documented. After a brief introduction to the basic physics of STIRAP, the central role of the method in the formation of ultracold molecules is discussed, followed by a presentation of how precision experiments (measurement of the upper limit of the electric dipole moment of the electron or detecting the consequences of parity violation in chiral molecules) or chemical dynamics studies at ultralow temperatures benefit from STIRAP. Next comes the STIRAP-based control of photons in cavities followed by a group of three contributions which highlight the potential of the STIRAP concept in classical physics by presenting data on the transfer of waves (photonic, magnonic and phononic) between respective waveguides. The works on ions or ion strings discuss options for applications, e.g. in quantum information. Finally, the success of STIRAP in the controlled manipulation of quantum states in solid-state systems, which are usually hostile towards coherent processes, is presented, dealing with data storage in rare-earth ion doped crystals and in nitrogen vacancy (NV) centers or even in superconducting quantum circuits. The works on ions and those involving solid-state systems emphasize the relevance of the results for quantum information protocols. Part B deals with theoretical work, including further concepts relevant to quantum information or invoking STIRAP for the manipulation of matter waves. The subsequent articles discuss the experiments underway to demonstrate the potential of STIRAP for populating otherwise inaccessible high-lying Rydberg states of molecules, or controlling and cooling the translational motion of particles in a molecular beam or the polarization of angular-momentum states. The series of articles concludes with a more speculative application of STIRAP in nuclear physics, which, if suitable radiation fields become available, could lead to spectacular results., Journal of Physics B: Atomic, Molecular and Optical Physics, 52 (20), ISSN:1361-6455, ISSN:0368-3508, ISSN:0953-4075, ISSN:0022-3700

16 pags., 10 figs. 5 tabs., 1 app., A full dimensional Potential Energy Surface (PES) of the CO + N2 system has been generated by extending an approach already reported in the literature and applied to N2-N2 (Cappelletti et al., 2008), CO2-CO2 (Bartolomei et al., 2012), and CO2-N2 (Lombardi et al., 2016b) systems. The generation procedure leverages at the same time experimental measurements and high-level ab initio electronic structure calculations. The procedure adopts an analytic formulation of the PES accounting for the dependence of the electrostatic and non-electrostatic components of the intermolecular interaction on the deformation of the monomers. In particular, the CO and N2 molecular multipole moments and electronic polarizabilities, the basic physical properties controlling the behavior at intermediate and long-range distances of the interaction components, were made to depend on relevant internal coordinates. The formulated PES exhibits substantial advantages when used for structural and dynamical calculations. This makes it also well suited for reuse in Open Molecular Science Cloud services., The authors thank MIUR and Perugia University for financial support through the AMIS project (Dipartimenti di Eccellenza 2018–2022). Financial support from VII FP (Egi-Inspire, Phys4Entry) and COST (Action CM901) is acknowledged. AaL and FP thank the Italian MIUR for funding through the program PRIN 2015 (contract 2015F59J3R_002). AaL also thanks the Dipartimento di Chimica, Biologia e Biotecnologie for funding under the program Fondo Ricerca di Base 2017. The work was also financially supported by Fondazione Cassa Risparmio Perugia (Codice Progetto: 2015.0331.021 Ricerca Scientifica e Tecnologica). MB was supported by the Ministerio de Ciencia, Innovación y Universidades (Spain, grant FIS2017-84391-C2-2-P). Calculations have been made possible by the support of the Virtual Organization COMPCHEM and allocated computing time from the OU Supercomputing Center for Education & Research (OSCER) at the University of Oklahoma (OU).

LaF3/SrF2 multilayer heterostructures with thicknesses of individual layers in the range 5-100 nm have been grown on MgO(100) substrates using molecular beam epitaxy. The longitudinal conductivity of the films has been measured using impedance spectroscopy in the frequency range 10-1-106 Hz and a temperature range 300-570 K. The ionic DC conductivities have been determined from Nyquist impedance diagrams and activation energies from the Arrhenius- Frenkel equation. An increase of the DC conductivity has been observed to accompany decreased layer thickness for various thicknesses as small as 25 nm. The greatest conductivity has been shown for a multilayer heterostructure having thicknesses of 25 nm per layer. The structure has a conductivity two orders of magnitude greater than pure LaF3 bulk material. The increasing conductivity can be understood as a redistribution of charge carriers through the interface due to differing chemical potentials of the materials, by strong lattice-constant mismatch, and/or by formation of a solid La1-xSrxF3-x solution at the interface during the growth process. © 2016 The Author(s).

The understanding of soot formation in combustion processes and the optimization of practical combustion systems require in situ measurement techniques that can provide important characteristics, such as particle concentrations and sizes, under a variety of conditions. Of equal importance are techniques suitable for characterizing soot particles produced from incomplete combustion and emitted into the environment. Additionally, the production of engineered nanoparticles, such as carbon blacks, may benefit from techniques that allow for online monitoring of these processes. In this paper, we review the fundamentals and applications of laser-induced incandescence (LII) for particulate diagnostics in a variety of fields. The review takes into account two variants of LII, one that is based on pulsed-laser excitation and has been mainly used in combustion diagnostics and emissions measurements, and an alternate approach that relies on continuous-wave lasers and has become increasingly popular for measuring black carbon in environmental applications. We also review the state of the art in the determination of physical parameters central to the processes that contribute to the non-equilibrium nanoscale heat and mass balances of laser-heated particles; these parameters are important for LII-signal analysis and simulation. Awareness of the significance of particle aggregation and coatings has increased recently, and the effects of these characteristics on the LII technique are discussed. Because of the range of experimental constraints in the variety of applications for which laser-induced incandescence is suited, many implementation approaches have been developed. This review discusses considerations for selection of laser and detection characteristics to address application-specific needs. The benefits of using LII for measurements of a range of nanoparticles in the fields mentioned above are demonstrated with some typical examples, covering simple flames, internal-combustion engines, exhaust emissions, the ambient atmosphere, and nanoparticle production. We also remark on less well-known studies employing LII for particles suspended in liquids. An important aspect of the paper is to critically assess the improvement in the understanding of the fundamental physical mechanisms at the nanoscale and the determination of underlying parameters; we also identify further research needs in these contexts. Building on this enhanced capability in describing the underlying complex processes, LII has become a workhorse of particulate measurement in a variety of fields, and its utility continues to be expanding. When coupled with complementary methods, such as light scattering, probe-sampling, molecular-beam techniques, and other nanoparticle instrumentation, new directions for research and applications with LII continue to materialize.

We have recently demonstrated a general and sensitive method to study low energy collisions that exploits the unique properties of a molecular synchrotron (Van der Poel et al., Phys Rev Lett 120:033402, 2018). In that work, the total cross section for ND3 + Ar collisions was determined from the rate at which ammonia molecules were lost from the synchrotron due to collisions with argon atoms in supersonic beams. This paper provides further details on the experiment. In particular, we derive the model that was used to extract the relative cross section from the loss rate, and present measurements to characterize the spatial and velocity distributions of the stored ammonia molecules and the supersonic argon beams.

We have recently demonstrated a general and sensitive method to study low energy collisions that exploits the unique properties of a molecular synchrotron (Van der Poel et al., Phys Rev Lett 120:033402, 2018). In that work, the total cross section for ND3 + Ar collisions was determined from the rate at which ammonia molecules were lost from the synchrotron due to collisions with argon atoms in supersonic beams. This paper provides further details on the experiment. In particular, we derive the model that was used to extract the relative cross section from the loss rate, and present measurements to characterize the spatial and velocity distributions of the stored ammonia molecules and the supersonic argon beams.

We present a novel slowing scheme for beams of laser-coolable diatomic molecules reminiscent of Zeeman slowing of atomic beams. The scheme results in efficient compression of the 1-dimensional velocity distribution to velocities trappable by magnetic or magneto-optical traps. 3D Monte Carlo simulations for the prototype molecule $^{88}\mathrm{Sr}^{19}\mathrm{F}$ and experiments in an atomic testbed demonstrate a performance comparable to traditional atomic Zeeman slowing and an enhancement of flux below v=35 m/s by a factor of $\approx 20$ compared to white-light slowing. This is the first experimentally shown continuous and dissipative slowing technique in molecule-like level structures, promising to provide the missing link for the preparation of large ultracold molecular ensembles., Comment: 4 figures

A Stark decelerator produces beams of molecules with high quantum state purity, and small spatial, temporal and velocity spreads. These tamed molecular beams are ideally suited for high-resolution crossed beam scattering experiments. When velocity map imaging is used, the Stark decelerator allows the measurement of scattering images with unprecedented radial sharpness and angular resolution. Differential cross sections must be extracted from these high-resolution images with extreme care, however. Common image analysis techniques that are used throughout in crossed beam experiments can result in systematic errors, in particular in the determination of collision energy, and the allocation of scattering angles to observed peaks in the angular scattering distribution. Using a high-resolution data set on inelastic collisions of velocity-controlled NO radicals with Ne atoms, we describe the challenges met by the high resolution, and present methods to mitigate or overcome them. PACS Codes: 34.50.-s; 37.10.Mn

521 p. DNA and proteins are involved in biological processes which make possible life. On the one hand, the four DNA bases constitute the alphabet of life. Their normal appearance includes stacked Watson-Crick pairs in order to form DNA strands, reinforced by the existence of the sugar backbone. However, the appearance of unusual structures, such as Hoogsteen pairs, triplexes and quadruplexes, raises the question of which are the intrinsic preferences of the DNA aggregation. On the other hand, proteins are chains of amino acids, whose interactions with DNA strands are the basis of the nucleosome formation. The mechanism which guides the nucleosome formation is still bewildering. The first goal of this thesis is the characterization of the non-covalent interactions in biological species and their aggregates by a combination of DFT calculations and Non-Covalent Interaction approach. The second goal is the elaboration of a reductionist model applying theoretical calculations, based in amino acid-DNA base interactions, in order to explain the leading mechanism of the histone-DNA formation. Finally, the third goal is the study of the intrinsic preferences of the DNA base self-aggregation process, analyzing the tautomerical landscape of the DNA bases, focusing on the competition between hydrogen bond and dispersive contributions. A combination of theoretical calculations and spectroscopic techniques has been used to understand the self-aggregation of purines (guanine) and pyrimidines (cytosine) in gas phase.

Amino acids are essential building blocks of life, and fluorinated derivatives have gained interest in chemistry and medicine. Modern mass spectrometry has enabled the study of oligo‐ and polypeptides as isolated entities in the gas phase, but predominantly as singly or even multiply charged species. While laser desorption of neutral peptides into adiabatically expanding supersonic noble gas jets is possible, UV–VIS spectroscopy, electric or magnetic deflectometry as well as quantum interferometry would profit from the possibility to prepare thermally slow molecular beams. This has typically been precluded by the fragility of the peptide bond and the fact that a peptide would rather ‘fry’, i.e. denature and fragment than ‘fly’. Here, we explore how tailored perfluoroalkyl functionalization can reduce the intermolecular binding and thus increase the volatility of peptides and compare it to previously explored methylation, acylation and amidation of peptides. We show that this strategy is essential and enables the formation of thermal beams of intact neutral tripeptides, whereas only fragments were observed for an extensively fluoroalkyl‐decorated nonapeptide. © 2017 The Authors. Journal of Mass Spectrometry Published by John Wiley & Sons Ltd.

The recent observation of propylene oxide in the interstellar medium has raised unusually large interest in view of the prototypical role that this molecule plays in chemical and biophysical investigations of chirality, a phenomenon that transversely pervades modern science for implications ranging from the mechanism of the origin and early evolution of life (homochirality) to key aspects of industrial and pharmaceutical chemistry, such as asymmetric synthesis. Here we present a survey of recent advances, designing and illustrating a number of possible experiments for the demonstration of chiral effects in the dynamics of the intermolecular interactions, suggesting a scenario for a stereo-directional origin of chiral discrimination.

332 p. En el presente proyecto de tesis un nuevo modus operandi es descrito, siendo este aplicable a estudios de propiedades químicas fundamentales y la generación de conocimiento base. Estos conocimientos fundamentales son en numerosas ocasiones el sustento para la realización de proyectos de investigación más aplicados. En concreto la tesis se centra en la determinación estructural y el análisis de interacciones no-covalentes. Estas fuerzas, difícilmente observables con la mayoría de técnicas, son las responsables de controlar una infinidad de características, empezando por la tremenda selectividad de las reacciones bioquímicas hasta ser en parte responsables de las propiedades de algunos polímeros, etc. La técnica experimental utilizada para la determinación estructural es la espectroscopia laser con resolución de masas, esta técnica permite el estudio de sistemas aislados generados a la carta, de este modo es posible el análisis de una amplia gama de agregados obteniendo de manera selectiva la contribución de cualquier pequeña modificación. Entre los sistemas estudiados se encuentran: La Glucosa (sistema modelo de moléculas flexible), un péptido (Treonina-Alanina-Alanina) y un polímero con base de antraceno (sistema modelo para el estudio de foldameros) y Los agregados de teobromina (como modelo para las etapas iniciales en procesos de nucleación). Finalizando con una amalgama de resultados experimentales que mezclan estas tres tipos de metodologías. Además se han implementado avances en el cálculo teórico y en diseño del sistema experimental.

Epitaxial layers of insulating binary lanthanide oxides have been considered as potential alternative to conventional SiO2 for gate dielectric application in future Si-based MOSFET devices, which was investigated in more detail for epitaxial Gd2O3 and Nd2O3 as model systems. Additionally, the ability to integrate epitaxial dielectric barrier layers into Si structures can usher also in a variety of novel applications involving oxide/silicon/oxide heterostructures in diverse nanoelectronic and quantum-effect devices. Although epitaxial layers of such ionic oxides with excellent structural quality can be grown using molecular beam epitaxy, they often exhibit poor electrical properties such as high leakage current density, flat band instability, poor reliability etc. owing to the presence of electrically active charge defects, generated either during the oxide layer growth or typical subsequent CMOS process steps. Based on the origin and individual character of these defects, we review various aspects of defect prevention and passivation which lead to a significant improvement in the dielectric properties of the heterostructures. Copyright © Materials Research Society 2017

We propose a number of possible experiments for the search of the enantioselective effects in the collision dynamics and intermolecular interactions of chiral molecules, suggesting a possible mechanism for chiral discrimination induced by molecular collisions.

Great success has been achieved in the modeling of gas-surface elementary processes by the use of the Born-Oppenheimer approximation. However, in metal surfaces low energy electronic excitations are generated even by thermal and hyperthermal molecules due to the absence of band gaps in the electronic structure. This shows the importance of performing dynamical simulations that incorporate non-adiabatic effects to analyze in which way they affect most common gas-surface reactions. Here we review recent theoretical developments in this problem and their application to the study of the effect of electronic excitations in the adsorption and relaxation of atoms and molecules in metal surfaces, in scattering processes, and also in recombinative processes between impinging atoms and adsorbates at the surface. All these studies serve us to establish what properties of the gas-surface interaction favor the excitation of low-energy electron-hole pairs. A general observation is that the nature of these excitations usually requires long lasting interactions at the surface in order to observe deviations from the adiabatic behaviour. We also provide the basis of the local density friction approximation (LDFA) that have been used in all these studies, and show how it has been employed to perform ab initio molecular dynamics with electronic friction (AIMDEF). As a final remark, we will shortly review on recent applications of the LDFA to successfully simulate desorption processes induced by intense femtosecond laser pulses., The authors acknowledge financial support by the Gobierno Vasco-UPV/EHU project IT756-13 and the Spanish Ministerio de Economía y Competitividad Grant No. FIS2016-76471-P.

The observation of hydrogen peroxide in the interstellar medium represents a remarkable discovery for the astrochemistry community. The prototypical role that this molecule, arguably the simplest chiral molecule, plays in the evolution of life in biospheres, is related to the chirality change transitions associated with the torsional motions around the O – O and the S – S bonds. In this paper, we present an overview on the state-of-art of possible experiments to demonstrate chiral effects discrimination and computational tools applied to peroxides and persulfides.

In this thesis, we detail an investigation into the photodissociation dynamics and spectroscopy of three atmospherically relevant chemical species: acetone, ethane (C2H6) and nitrous oxide (N2O). A systematic study into the photodissociation mechanisms of acetone has been carried out across its first electronically excited state, covering a wavelength range of 230 - 312nm. The photodissociation of acetone comprises primary and secondary dissociation mechanisms, involving one and two C−C bond ruptures. At wavelengths longer than 306nm, we have discovered a novel dissociation pathway, involving a barrierless dissociation to CH3CO + CH3, reproduced by a statistical prior model. We estimate this mechanism will account for 83% of CH3 formed by absorption of actinic radiation. The remaining 17% is accounted by dissociation in the T1 state, which dominates at wavelengths shorter than 306nm. This reaction channel was readily modelled by a statistically adiabatic-impulsive (SAI) model. At wavelengths shorter than 263 nm, secondary dissociation of acetone can occur. The CH3CO fragment from the primary step undergoes dissociation, yielding CH3 + CO. We refute the roaming mechanism believed to occur in this wavelength region, and the only two pathways observed are the primary and secondary dissociation reactions. High level electronic structure calculations have been undertaken to determine the ionisation energies and dynamics of ethane. Using the HEAT345(Q) procedure, we determine adiabatic ionisation energies for the 2Eg and 2A1g states to be 11.52 and 11.56 eV respectively, with an estimated uncertainty of 0.025 eV. The photoelectron spectrum of C2H6 has also be simulated using a quadratic model vibronic coupling Hamiltonian, comprising the two lowest-lying electronic states of C2H+6 . The linear coupling model reproduces the spectral envelope, and a quadratic model is required for quantitative agreement with the reference spectrum. The O 1D photofragment yield from the photodissociation of N2O, N2O−N2O and N2O−O2 have been measured over the wavelength range 206 - 216 nm. we observe no difference in the UV absorption properties between these three species, contrary to theoretical simulations. A new photodissociation channel has also been discovered in the N2O−O2 complex, producing O 3P fragments. A spin-flip mechanism is proposed to account for this reaction.

Microwave spectroscopy probes the rotational transitions of polar molecules in the gas phase and is a proven technique for the detection and identification of short-lived molecules produced from a variety of molecular sources. In this explorative study, we demonstrate that two prerequisites can be met for microwave spectroscopy to become a quantitative tool for the analysis of high-temperature gas mixtures as found in combustion environments. First, we show that the rotational temperature of the targeted species can be sufficiently cooled to allow for a sensitive detection of low-lying rotational states after sampling from hot (∼2200 K) flames. Second, we show that signal intensity profiles can be assembled which, after correcting for the different flame temperatures at various sampling positions, agree well with mole fraction profiles obtained via flame-sampling molecular-beam mass spectrometry. Based on the described results, it is conceivable that rotational spectroscopy can contribute towards the unraveling of complex, high-temperature reaction networks. DFG/KO 1363/31-1 Land Niedersachsen

© 2015 by Annual Reviews. All rights reserved. The field of cold molecules has become an important source of new insight in fundamental chemistry and molecular physics. High resolution spectroscopy benefits from translationally and internally cold molecules by increased interaction times and reduced spectral congestion. Completely new effects in scattering dynamics become accessible with cold and controlled molecules. Many of these experiments use molecular beams as a starting point for the generation of molecular samples. This review gives an overview of methods to produce beams of cold molecules starting from supersonic expansions or effusive sources and provides examples of applications in spectroscopy and molecular dynamics studies.

Van der Waals molecules are complexes of two or more atoms or molecules bound by weak intermolecular forces rather than a conventional chemical bond. This thesis contains a high resolution molecular beam study of the rotational spectra of two such species, ArNO and NeNO. A new hamiltonian is presented to account for the spectra of these open-shell complexes. The theory is similar to that already known for the uncomplexed diatom, nitric oxide, but is modified to an asymmetric top form appropriate for these non-linear species. Two novel interactions require inclusion. The first models a slight quenching of the NO orbital angular momentum by the rare gas atoms. The second is a large centrifugal distortion associated with the effects of the bending motion on the projection of the electronic angular momentum on the complex's a-inertial axis. A comparatively rich, though incomplete, spectrum is obtained for ArNO. Most of the transitions that originate from the lower rotational states are assigned and fitted to within a few MHz using the modified open-shell hamiltonian. Possible sources are suggested for the origins of the small residual errors between the observed and calculated transition frequencies. A vibrationally-averaged structure is derived from the fitted molecular parameters indicating an equilibrium geometry which is quite close to a T-shape. The hyperfine structure in the spectrum which is associated with the 14 N nucleus is well fitted by the hamiltonian; however, the magnetic hyperfine parameters are significantly perturbed from the values that best fit the lambda-doubling spectrum of the uncomplexed diatom. The implications of this with respect to the nature of the rare gas-nitric oxide intermolecular interaction are discussed. Greater experimental difficulties are encountered in trying to record the radiofrequency and microwave spectrum of NeNO and so fewer transitions have been measured than for ArNO. A partial analysis yields approximate values for the structural parameters. The complex exhibits a larger deviation from the T-shaped geometry than is observed for ArNO. The spectrum also provides an estimate of the magnitude of the quenching of the orbital angular momentum. The quenching interaction is somewhat larger in the neon complex.

Supersonic beams are a prevalent source of cold molecules utilized in the study of chemical reactions, atom interferometry, gas-surface interactions, precision spectroscopy, molecular cooling and more. The triumph of this method emanates from the high densities produced in relation to other methods, however beam density remains fundamentally limited by interference with shock waves reflected from collimating surfaces. Here we show experimentally that this shock interaction can be reduced or even eliminated by cryo-cooling the interacting surface. An increase in beam density of nearly an order of magnitude was measured at the lowest surface temperature, with no further fundamental limitation reached. Visualization of the shock waves by plasma discharge and reproduction with direct simulation Monte Carlo calculations both indicate that the suppression of the shock structure is partially caused by lowering the momentum flux of reflected particles, and significantly enhanced by the adsorption of particles to the surface. We observe that the scaling of beam density with source pressure is recovered, paving the way to order of magnitude brighter cold molecular beams., 10 pages, 6 figures

In this paper, we introduced a new different thin film deposition method for heavily carbon doped GaAs. Used method is thermionic vacuum arc (TVA) and first used for the carbon doping process. The method is very fast deposition process for the other growth method such as metal organic chemical vapor deposition, molecular beam epitaxy, molecular organic molecular beam epitaxy. The smallest grain size of GaAs and doped GaAs were obtained by carbon doping process. Mean crystalline size and height of crystalline size were found to be 3.4 nm and 4 nm, respectively. Crystal direction was found to be (022) plane and (024) plane for the sample at 45.322° and 75.060°, respectively. The production process and obtained results show that used methods is very simple, low cost, eco friendly and very fast method for the carbon doped GaAs. © 2015 Elsevier B.V.

Isothermal kinetic measurements of 15NO reduction with CO on Pd(111) surfaces were carried out under net-oxidizing conditions with 15NO + CO + O2, using a molecular beam instrument (MBI). Transient state (TS) and steady state (SS) kinetic details of the above reaction were obtained for a wide range of temperature and beam compositions, especially with O2-rich compositions. Increasing O2 content, generally, suppresses 15NO reduction in the SS; nonetheless, irrespective of O2 content, 15N2 was produced in TS, and to a significant extent under SS conditions too. Sustainable N 2 production between 450 and 600 K and with low to moderate amount of oxygen was observed, and the extent of NO decomposition was also quantified. The ratio of 15N2:15N2O was generally found to be around 8:1 under most of the reaction conditions. Maxima in the SS reaction rates of all products were observed between 500 and 600 K. Compared to other elementary reaction steps, a slow decay observed with N + N ? N2 step under SS beam oscillation conditions demonstrates its contribution to the rate limiting nature of the overall reaction. Fast beam switching experiments have been performed alternately between O2-lean and -rich conditions, thus highlighting the effectiveness of 15NO reduction in TS, irrespective of the beam composition. Possibly in a future technology initiative, this aspect could be exploited to manage more 15NO reduction on Pd-based catalysts. � 2011 American Chemical Society.

We report details of the design and operation of a single apparatus that combines Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy with vacuum ultraviolet (VUV) photoionization Time-of-Flight Mass Spectrometry (TOFMS). The supersonic expansion used for cooling samples is interrogated first by passing through the region between two microwave horns capable of broadband excitation and detection in the 2-18 GHz frequency region of the microwave. After passing through this region, the expansion is skimmed to form a molecular beam, before being probed with 118 nm (10.5 eV) single-photon VUV photoionization in a linear time-of-flight mass spectrometer. The two detection schemes are powerfully complementary to one another. CP-FTMW detects all components with significant permanent dipole moments. Rotational transitions provide high-resolution structural data. VUV TOFMS provides a gentle and general method for ionizing all components of a gas phase mixture with ionization thresholds below 10.5 eV, providing their molecular formulae. The advantages, complementarity, and limitations of the combined methods are illustrated through results on two gas-phase mixtures made up of (i) three furanic compounds, two of which are structural isomers of one another, and (ii) the effluent from a flash pyrolysis source with o-guaiacol as the precursor.We report details of the design and operation of a single apparatus that combines Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy with vacuum ultraviolet (VUV) photoionization Time-of-Flight Mass Spectrometry (TOFMS). The supersonic expansion used for cooling samples is interrogated first by passing through the region between two microwave horns capable of broadband excitation and detection in the 2-18 GHz frequency region of the microwave. After passing through this region, the expansion is skimmed to form a molecular beam, before being probed with 118 nm (10.5 eV) single-photon VUV photoionization in a linear time-of-flight mass spectrometer. The two detection schemes are powerfully complementary to one another. CP-FTMW detects all components with significant permanent dipole moments. Rotational transitions provide high-resolution structural data. VUV TOFMS provides a gentle and general method for ionizing all components of a gas phase mixture with ionization thresholds below 10.5 eV, p...

Reflectance anisotropy spectroscopy (RAS) is demonstrated to be particularly suitable for studying the deposition of organic epitaxial layers in ultrahigh vacuum by organic molecular beam epitaxy, thanks to its high sensitivity and applicability in situ. In the case of α-quaterthiophene, both homoepitaxy and heteroepitaxy have been monitored, demonstrating the crystallinity of the films up to tens of monolayers and the epitaxial relation to the substrate. In both cases, optical RAS data are compared to the results of ex situ characterization of the same samples by atomic force microscopy.© 2009 American Vacuum Society

A series of precise electric deflection experiments were done on a supersonic beam of toluene molecules in several expansion conditions and field strengths. We analyzed the effect of a gradual rotational cooling on the evolution of the beam profile by use of the available theories of asymmetric-top dipoles in electric fields. We have recorded from non-broadened (warm) to very broad and asymmetric (cold) profiles, and discussed this effect in terms of the Stark perturbation on the rotational motion. Fil: Carrera, Alvaro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Mobbili, Marcos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Moriena, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Marceca, Ernesto José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

Recent experimental and theoretical advances in the study of the dissociation of excited molecules are revealing unexpected mechanisms, when their outcomes are tackled by combining (i) space-time ion imaging of translational features, with (ii) spectroscopic probing of rotational and vibrational distributions; crucial is the assistance of (iii) the quantum chemistry of structural investigations of rearrangements of chemical bonds, and of (iv) the simulations of molecular dynamics to follow the evolution of selective bond stretching and breaking. Here we present results of such an integrated approach to methyl formate, HCOOCH3, the simplest of esters; the main focus is on the rotovibrationally excited CO (v = 1) product and in general on the energy distribution in the fragments. Previous laser studies of dissociation into CO and CH3OH at a sequence of various wavelengths discovered signatures of a roaming mechanism by the late arrival of CO (v = 0) products in time-of-flight ion imaging. Subsequent detailed investigations as a function of excitation energy provided the assessment of the threshold, which opens for triple breakdown into CO and further fragments H and CH3O, as spectroscopically characterized by ion imaging and FTIR respectively. Accompanying quantum mechanical electronic structure calculations and classical molecular dynamics simulations clarify the origin of these fragments through “roaming” pathways involving incipient radical intermediates at energies below the triple fragmentation threshold: a specific role is played by nonadiabatic transitions at a conical intersection between ground and excited states; alternative pathways focalize our attention to regions of the potential energy surfaces other than those in the neighbourhoods of saddle points along minimum energy paths: eventually this leads us to look for avenues in reaction kinetics beyond those of venerable transition state theories.

Former calculations showed that atomic N incident at energies of a few eV on N-covered Ag(1 1 1) forms N2 molecules by the Eley-Rideal (ER) mechanism, i.e. by direct pick-up of adsorbates. Here, we calculate the azimuthal angle distributions and the rovibrational energies of those ER products. We observe a non-trivial angle dependence that may result in very low in-plane ER yield for some given incident azimuthal angles. We find that most of the energy released upon NN bond formation, about 7 eV, is stored in the rovibrational degrees of freedom independently of the incidence energy considered., This work has been supported in part by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-02) and the European Commission (Grant No. FP7-PEOPLE-2010-RG276921).

The rotational spectrum of piperazine has been investigated by free jet absorption millimeter wave spectroscopy. The spectrum of the polar conformer with axial–equatorial orientations of the two amino hydrogens was only observed. This assignment was confirmed by the spectra of the two monodeuterated and the bideuterated species. Ab initio and density functional calculations predict the observed conformer to have an energy intermediate between the equatorial–equatorial and axial–axial non-polar forms, the former species being the global minimum.

The Fourier transform rotational spectra of the normal and the 13 C species of the 1:1 complex between difluoromethane and water have been measured. The rotational transitions are split into two component lines, due to the internal rotation of the water moiety. The barrier to this motion has been estimated to be 340(20) cm −1 . An improved structure of the complex has been obtained.

The changes in the surface composition of a Pt(50)Rh(50)(100) alloy due to an ongoing 2H(2) + O(2)--2H(2)O chemical reaction have been studied in situ. Exploiting the high-energy resolution and surface sensitivity of synchrotron radiation core-level spectroscopy it was possible to monitor the population of the two transitions metals atoms at the gas-surface interface. Sequences of fast high-resolution core-level spectra of the Rh3d(5/2), Pt4f(7/2), and O1s core levels showed a continuous exchange of atoms between the first and subsurface layers. An unexpected Pt surface enrichement was found under slightly oxidizing conditions, opposite to what found in a highly oxidizing atmosphere.

We describe a stable kHz rate laser ablation/desorption supersonic molecular beam source for use in kHz rate laser experiments. With the development of modern lasers that typically operate at kHz rates, a need has arisen for stable molecular beam laser ablation/desorption sources for the study of involatile species. Many biomolecules of interest cannot be brought into the gas phase without thermal decomposition by simply heating the substrate and most (especially refractory) metals have melting and boiling points that are impossible to reach with conventional ovens. The source is based upon strong nonresonant interaction of a dithering laser focus with a rotating and translating solid rod, hydrodynamic transport of the ablated/desorbed material in helium or argon, and subsequent supersonic expansion. Further design details include flexible and easy adjustment of the source for rapid prototyping and optimization for kHz rate performance. Due to the high rate of sample removal, a major concern is clogging of the nozzle and laser input channel due to both material condensation and debris formation. In order to illustrate the range of applications, we demonstrate (1) the kHz laser ablation of a high temperature refractory metal (niobium) for use in studies of metal clusters; and (2) the kHz laser desorption and jet cooling of an involatile biomolecule (the DNA base guanine) for use in spectroscopic and dynamical studies. This kHz source design has been shown to be stable for over 12 continuous hours of operation (>4×107(>4×107 laser shots) and can be readily scaled to even higher repetition rates (>10 kHz).

El objetivo de esta tesis es estudiar, a escala molecular, la interacción de una molécula modelocon un número peque˜no y controlado de moléculas de solvente capaces de formar uniones H. Se haelegido como prueba a la molécula de cresol, ya que es capaz de participar en la red de uniones H, y al mismo tiempo posee una región hidrofóbica (anillo aromático y grupo metilo) cuya interacción se desea investigar. Los sistemas elegidos para tal fin son clusters binarios formados por una molécula de p-cresol u o-cresol embebida en un número peque˜no (entre 1 y 8) de moléculas de agua y/o amoníaco. También se evalúa la existencia de procesos reactivos, como la tranferencia de carga del solutoal solvente a escala molecular, en función de la cantidad de moléculas de solvente presentes en el cluster. La técnica experimental utilizada fue la deflexión eléctrica en haces moleculares, asistida pordiversas herramientas de cálculo como: métodos basados en el cálculo de estructura electrónica,simulaciones clásicas de dinámicas en campos eléctricos, dinámicas en campos de fuerza clásicos ydinámicas cuánticas. Los experimentos fueron realizados en diferentes condiciones, de manera de poder caracterizara los clusters cuando son rígidos y cuando son flexibles. En esta última condición, se obtuvieronvalores de susceptibilidad eléctrica de las diferentes familias de clusters en función de la cantidad de moléculas de solvente que forman el mismo. A partir de esas medidas se determinó el momento dipolar de dichas partículas. Estas propiedades nos permitieron revelar características estructurales y dinámicas del entorno de solvatación del cresol. The goal of this thesis is to study, at a molecular level, the interaction of a model molecule with a small and controlled number of solvent molecules capables of forming H bonds. The test molecule is cresol, since it can share H bonds, and at the same time has a hydrophobic region (aromatic ring and methyl group), whose interaction we wish to investigate. The system chosen to perform the experiments are binary clusters, composed by a molecule of p-cresol or o-cresol immersed in a small number (1 to 8) of water or ammonia molecules. We also study the existence of reactive processes, like the charge transfer to solvent at themolecular scale, as a function of the amount of solvent molecules present in the cluster. The experimental technique used is the electric deflection in molecular beams, together withseveral computational calculations, such as: methods based in the calculation of electronic structure, molecular mechanics in electric fields, molecular mechanics in classic force fileds and quantum dynamics. The experiments were performed in several different conditions, as a mean to characterize theclusters when they are rigid and when they are flexible. In this latter case, we obtained electric susceptibility values for the different clusters families as a function of the solvent molecules. From these measurements, we determined the dipole moment of the particles. These properties allowed us to reveal structural and dynamical characteristics for the solvation environment of the cresol. Fil: Mobbili, Marcos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Iso-chloropropane dehydrohalogenation processes by alkali ion collisions (Li, Na and K) have been studied from a theoretical and an experimental point of view. Both methods have detected the following channels:(1): C(3)H(7)Cl + M(8)→ [C(3)H(6)M](+) + HCl; (2): C(3)H(7)Cl + M(+)→ C(3)H(6) + [HClM(]+); (3) :C(3)H(7)Cl + M(+)→ C(3)H(7) + MCl(+), where M represents the alkali ion. The first two reactions are dehydrohalogenations while the third one is a C-Cl bond heterolytic dissociation producing the alkali metal halide and C3H7+. Their reaction dynamics has been studied experimentally by molecular beam techniques while the theoretical research was carried out mainly by an exploration of potential energy surface (PES), a statistic study using direct dynamics as well as a RRKM analysis over the characterized PES. EXPERIMENTAL PART The described processes were studied using an octupolar radiofrequency-guided ion beam apparatus (RF-GIB) built in our lab. The alkali ions and iso-chloropropane in gas phase collide inside of octupolar reaction chamber at low pressures conditions where the reaction products are guided by a set of einzels lenses toward a mass spectrometer identifying the produced fragments. The obtention of the reactive cross section dependence as a function of collision energy for each channel and ion is the objective of this procedure. THEORETICAL PART The characterization of the PES, quasiclassical dynamics and RRKM study for the three alkali ions were performed in the theoretical part. The PES exploration and the possible reaction mechanisms was calculated by quantum chemistry using GAMESS 2008 package at MP2 level. The dynamics simulation was performed by Venus/NWChem, running on the fly classical trajectories. This software solves the classical equations of motion using the potential energy obtained from chemistry calculations, with the aim to calculate reactive cross sections. The visualization of pathways and a vibro-rotational analysis complete the dynamics study. Finally, the RRKM study allows to obtain a Kinetic Monte Carlo simulation. This model gives information about the several steps of the whole mechanism of the system and it complements the provided data by experimentation and the “on the fly” dynamics., S’han estudiat les reaccions de deshidrohalogenació del compost iso-cloropropà induïdes per col•lisió d’ions alcalins (Li, Na i K, representats per M) tant des d’un punt de vista teòric com experimental. Els canals detectats per ambdues vies són: :(1): C(3)H(7)Cl + M(8)→ [C(3)H(6)M](+) + HCl; (2): C(3)H(7)Cl + M(+)→ C(3)H(6) + [HClM](+); (3) :C(3)H(7)Cl + M(+)→ C(3)H(7) + MCl(+), En les dues primeres reaccions té lloc la pròpiament dita deshidrohalogenació i, en canvi, en el tercer cas es tracta d'una dissociació heterolítica de l’enllaç C-Cl amb la formació de l’halur del metall alcalí i del catió C(3)H(7)(+). A la part experimental s’ha realitzat un estudi de dinàmica de reacció mitjançant la tècnica dels feixos moleculars mentre que la part teòrica ha inclòs l’exploració de la superfície d’energia potencial (SEP) del procés, un estudi estadístic per dinàmica directa i un anàlisi RRKM sobre la SEP caracteritzada. Tanmateix, es comparen els citats resultats obtinguts experimentalment amb els del tractament teòric amb la finalitat d’establir validesa i grau de complementació entre ambdós procediments. A més, les simulacions teòriques permeten determinar els diferents mecanismes duts a terme per cada procés i la caracterització del camí de reacció sobre la SEP calculada. PART EXPERIMENTAL Experimentalment s’ha dut a terme l’estudi dels citats processos de deshidrohalogenació fent servir un aparell de feixos iònics guiats per radiofreqüència (Radiofrequency-guided ion beam, RF-GIB) octupolar construït al nostre laboratori. En aquest aparell els ions alcalins focalitzats per una sèrie de lents Einzel i guiats per un camp de radiofreqüència col•lisionen contra la mostra d’iso-cloropropà en fase gas allotjada a la cambra de reacció de l’octupol a baixa pressió. Un altre conjunt de lents d’einzels dirigeixen els productes cap a un espectròmetre de masses encarregat d’identificar-los en funció de la seva massa. L'objectiu experimental és caracteritzar la dependència de les seccions eficaces reactives en funció de l’energia de col•lisió per a cada canal de reacció i per els tres ions alcalins estudiats. PART TEÒRICA La part teòrica consta de la caracterització de la SEP dels processos, de la corresponent dinàmica clàssica “on the fly” i de l’estudi RRKM per a cadascun dels tres ions alcalins. L’exploració de la SEP ha estat realitzada mitjançant càlculs ab initio utilitzant el programa de química quàntica GAMESS 2008 sota el mètode post Hartree-Fock a nivell de teoria de pertorbacions de segon ordre MP2. Amb aquest procediment s’ha caracteritzat la topologia de les diferents SEP, així com els seus possibles mecanismes de reacció els quals han permès justificar els resultats obtinguts experimentalment. La dinàmica “on the fly” utilitza el software Venus/NWChem el qual simula la reacció de deshidrohalogenació estudiada experimentalment mitjançant trajectòries clàssiques. Aquest software simula la col•lisió per medi de la mecànica newtoniana (Venus) obtenint l’energia potencial d’interacció per mètodes de química quàntica (NWChem) a cada pas d’integració i fent servir DFT. Mitjançant aquest procediment es simula un nombre suficientment gran de trajectòries amb l'objectiu de confeccionar una estadística fiable, calcular reactivitats i seccions eficaces reactives per a ser comparades amb els resultats experimentals, així com la visualització del camí de reacció pres a cada canal i per a cadascun dels tres ions alcalins. Finalment, l’obtenció de constants de velocitat per mitjà d’un estudi RRKM condueix a realitzar una simulació pel mètode Kinetic Monte Carlo. Aquest estudi proporciona informació sobre l’evolució del sistema entre les diverses etapes del mecanisme global fins assolir condicions estacionaries i complementa la informació proporcionada per l’experimentació i la dinàmica “on the fly”.