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This work shows how the N 1s photoemission (PE) spectrum of self-associated melamine molecules in aqueous solution has been successfully rationalized using an integrated computational approach encompassing classical metadynamics simulations and quantum calculations based on density functional theory (DFT). The first approach allowed us to describe interacting melamine molecules in explicit waters and to identify dimeric configurations based on π–π and/or H-bonding interactions. Then, N 1s binding energies (BEs) and PE spectra were computed at the DFT level for all structures both in the gas phase and in an implicit solvent. While pure π-stacked dimers show gas-phase PE spectra almost identical to that of the monomer, those of the H-bonded dimers are sensibly affected by NH···NH or NH···NC interactions. Interestingly, the solvation suppresses all of the non-equivalences due to the H-bonds yielding similar PE spectra for all dimers, matching very well our measurements.

The near-edge X-ray absorption fine structure (NEXAFS) spectra of indole, 2,3-dihydro-7-azaindole, and 3-formylindole in the gas phase have been measured at the carbon and nitrogen K-edges. The spectral features have been interpreted based on density functional theory (DFT) calculations within the transition potential (TP) scheme, which is accurate enough for a general description of the measured C 1s NEXAFS spectra as well as for the assignment of the most relevant features. For the nitrogen K-edge, the agreement between experimental data and theoretical spectra calculated with TP-DFT was not quite satisfactory. This discrepancy was mainly attributed to the many-body effects associated with the excitation of the core electron, which are better described using the time-dependent density functional theory (TDDFT) with the range separated hybrid functional CAM-B3LYP. An assignment of the measured N 1s NEXAFS spectral features has been proposed together with a complete description of the observed resonances. Intense transitions from core levels to unoccupied antibonding π* states as well as several transitions with mixed-valence/Rydberg or pure Rydberg character have been observed in the C and N K-edge spectra of all investigated indoles.

We report a combination of quantum mechanical calculations and a range of spectroscopic measurements in the gas phase of N,N-diethylhydroxylamine, an important scavenger compound. Three conformers were observed by pulsed jet Fourier transform microwave spectroscopy in the 6.5-18.5 GHz frequency range. They are characterized by the hydroxyl hydrogen atom being in trans orientation with respect to the bisector of the CNC angle while the side alkyl chains can be both trans (global minimum, Cs symmetry, A = 7608.1078(4), B = 2020.2988(2) and C = 1760.5423(2) MHz) or one trans and the other gauche (second energy minimum, A = 5302.896(1), B = 2395.9822(4) and C = 1804.8567(3) MHz) or gauche' (third energy minimum, A = 5960.8025(6), B = 2273.6627(4) and C = 1975.8074(4) MHz). For the global minimum, the 13Cα,13Cβ and 15N isotopologues were observed in natural abundance, allowing for an accurate partial structure determination. Moreover, several lines were detected by free jet absorption millimeter wave spectroscopy in the 59.6-74.4 GHz spectral range. The electron binding energies of the highest occupied molecular orbital and the next-to-highest occupied molecular orbital, determined by photoelectron spectroscopy, are 8.95 and 10.76 eV, respectively. Supporting calculations evidence that, (i) upon ionization of the HOMO, the molecular structure changes from an amine to an N-oxoammonium arrangement and (ii) the 0-0 of the HOMO-1 photoionization is 10.46 eV. The K-shell binding energies, determined by X-ray photoelectron spectroscopy, are 290.42 eV (Cβ), 291.45 eV (Cα), 405.98 eV (N) and 538.75 eV (O). The Fourier transform near infrared spectrum is reported and a tentative assignment is proposed. The equilibrium wavenumber (ω̃ = 3811 cm-1) and the anharmonicity constant (ω̃χ = -87.5 cm-1) of the hydroxyl stretching mode were estimated using a quadratic model.

The relaxation of photoexcited nanosystems is a fundamental process of light–matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free-electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental photoelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He∗) within 1 ps. Subsequently, the bubble collapses and releases metastable He∗ at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses., Funding from the Deutsche Forschungsgemeinschaft (MU 2347/8-1, STI 125/19-1, and the priority program 1840 QUTIF, the Carlsberg Foundation, National Science Foundation (DMR-1828019), Carl-Zeiss-Stiftung, Grant No. FIS2017-87801-P (AEI/FEDER, UE), and Swiss National Science Foundation (200020_162434) is gratefully acknowledged. O.G., D.M.N., and M.P.Z. were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division, through Contract No. DE-AC02-05CH11231.

The initial deactivation pathways of gaseous 2-nitrophenol excited at 268 nm were investigated by time-resolved photoelectron spectroscopy (TRPES) with femtosecond-VUV light, produced by a monochromatized high harmonic generation source. TRPES allowed us to obtain new, valuable experimental information about the ultrafast excited-state dynamics of 2-nitrophenol in the gas phase. In accord with recent ab initio on-The-fly nonadiabatic molecular dynamic simulations, our results validate the occurrence of an ultrafast intersystem crossing leading to an intermediate state that decays on a subpicosecond time scale with a branched mechanisms. Two decay pathways are experimentally observed. One probably involves proton transfer, leading to the most stable triplet aci-form of 2-nitrophenol; the second pathway may involve OH rotation. We propose that following intersystem crossing, an ultrafast fragmentation channel leading to OH or HONO loss could also be operative.

International audience; We investigate the orthorhombic distortion and the structural dynamics of epitaxial MnAs layers on GaAs(001) using static and time-resolved x-ray diffraction. Laser-induced intensity oscillations of Bragg reflections allow us to identify the optical phonon associated with orthorhombic distortion and to follow its softening along the path towards an undistorted phase of hexagonal symmetry. The frequency of this mode falls in the THz range, in agreement with recent calculations. Incomplete softening suggests that the $\beta-\gamma$ transformation deviates from a purely second-order displacive transition.

The investigation of ultrafast dynamics, taking place on the few to sub-picosecond time scale, is today a very active research area pursued in a variety of scientific domains. With the recent advent of X-ray free-electron lasers (XFELs), providing very intense X-ray pulses of duration as short as a few femtoseconds, this research field has gained further momentum. As a consequence, the demand for access strongly exceeds the capacity of the very few XFEL facilities existing worldwide. This situation motivates the development of alternative sub-picosecond pulsed X-ray sources among which femtoslicing facilities at synchrotron radiation storage rings are standing out due to their tunability over an extended photon energy range and their high stability. Following the success of the femtoslicing installations at ALS, BESSY-II, SLS and UVSOR, SOLEIL decided to implement a femtoslicing facility. Several challenges were faced, including operation at the highest electron beam energy ever, and achievement of slice separation exclusively with the natural dispersion function of the storage ring. SOLEIL's setup also enables, for the first time, delivering sub-picosecond pulses simultaneously to several beamlines. This last feature enlarges the experimental capabilities of the facility, which covers the soft and hard X-ray photon energy range. In this paper, the commissioning of this original femtoslicing facility is reported. Furthermore, it is shown that the slicing-induced THz signal can be used to derive a quantitative estimate for the degree of energy exchange between the femtosecond infrared laser pulse and the circulating electron bunch.

In this work, we show how to control the morphology of femtosecond laser melted gold nanosphere aggregates. A careful choice of both laser fluence and wavelength makes it possible to selectively excite different aggregate substructures to produce larger spherical nanoparticles, nanorods, and nanoprisms or necklace-like 1D nanostructures in which the nanoparticles are interlinked by bridges. Finite integral technique calculations have been performed on the near-field concentration of light in the nanostructures which confirm the wavelength dependence of the light concentration and suggest that the resulting localized high intensities lead to nonthermal melting. We show that by tuning the wavelength of the melting light it is possible to choose the spatial extension of the ensembles of NPs heated thus allowing us to exhibit control over the morphology of the nanostructures formed by the melting process. By a proper combination of this method with self-assembly of chemically synthesized nanoparticles, one can envisage the development of an innovative high-throughput high-resolution nanofabrication technique.

The X-ray absorption spectra (XAS) of Ar-2 and ArNe dimers and small Ar clusters in the L-2,L-3 region (244-252 eV) of the Ar atom have been recorded using synchrotron light and a combination of coincidence methods and kinetic energy discrimination of energetic ions. The absorption peaks in the spectra of the dimers and clusters were found to be shifted and broadened relative to the peaks in the spectrum of the Ar atom. In order to unambiguously relate these chemical shifts to the electronic structure of the core excited states in dimers, we performed ab initio calculations of the XAS spectra. Implications of the results for the use of XAS as a structure determination method in large rare gas clusters are discussed.

This paper presents the performance of a single-photon-counting hybrid pixel X-ray detector with synchrotron radiation. The camera was evaluated with respect to time-resolved experiments, namely pump–probe–probe experiments held at SOLEIL. The UFXC camera shows very good energy resolution of around 1.5 keV and allows the minimum threshold setting to be as low as 3 keV keeping the high-count-rate capabilities. Measurements of a synchrotron characteristic filling mode prove the proper separation of an isolated bunch of photons and the usability of the detector in time-resolved experiments.

We have investigated by time-resolved X-ray diffraction the manganese arsenide structure dynamics in MnAs/GaAs (001) epitaxial films, when the $\alpha \to \beta $ magnetostructural phase transition is triggered by an ultra-fast optical laser pulse. Understanding the photo-induced phase transition dynamics is relevant for applications of MnAs/GaAs (001) as a magnetically active template in laser-induced magnetization switching processes. The main goal of our experiment is to determine the timescales of the structural changes that are likely to play a role in laser-driven magnetization reversal.

We explore the possibility that protonated molecular ions might be an unexpected source of interference in the recognition process of anions and neutral species by Zn-salophen receptors. Zn-salophen complexes are known to bind anions and neutral molecules in solution. We present here evidence (from computational work and IRMPD spectroscopy) that these complexes can also be the binding site for protonated pyridine or quinuclidine. The resulting binding pattern does not involve the Zn ion, but one of the oxygen atoms directly attached to it. The resulting complex therefore turns out to have a positive charge adjacent to the Zn-salophen binding site. This finding seems to point to the existence of an interfering factor in the quantification of the experimental data about the association constant.

It was shown recently that the Fe magnetization reversal in the Fe/MnAs/GaAs(001) epitaxial system, attained by temperature control of the regular stripe pattern of the MnAs ?- and ?-phases, can also be driven by an ultrashort optical laser pulse. In the present time-resolved scattering experiment, we address the dynamics of the MnAs ?/? self-organized stripe pattern induced by a 100 fs optical laser pulse, using as a probe the XUV radiation from the FERMI free-electron laser. We observe a loss in the diffraction intensity from the ordered ?/? stripes that occurs at two characteristic timescales in the range of ~10-12 and ~10-10 s. We associate the first intensity drop with ultrafast electron-lattice energy exchange processes within the laser-MnAs interaction volume and the second with thermal diffusion towards the MnAs/GaAs interface. With the support of model calculations, the observed dynamics are interpreted in terms of the formation of a laterally homogeneous MnAs overlayer, the thickness of which evolves in time, correlating the MnAs microstructure dynamics with the Fe magnetization response.

Spintronic devices are most often controlled by applied magnetic fields or by the injection of spin-polarized currents.

Cisplatin and transplatin (cis- and trans-[PtCl2(NH3)2]) have been allowed to react with methionine (Met) in water solution in a study aimed to characterize the monofunctional complex primarily formed. The thioether function of methionine is known to have a very high affinity for square planar platinum(II) and sulfur-containing biomolecules have been proposed as a cisplatin drug reservoir on the way to platination at DNA. Both cisplatin and transplatin yield [PtCl(NH3)2Met]+ complexes, delivered by electrospray ionization in the gas phase and sampled as isolated species using tools based on mass spectrometry. The collision induced dissociation spectra of both cis-[PtCl(NH3)2Met]+ and trans-[PtCl(NH3)2Met]+ are quite similar and also the transport properties assayed by ion mobility mass spectrometry do not allow any appreciable discrimination. However, the vibrational spectra obtained by IR multiple photon absorption (IRMPD) spectroscopy show distinct features. Their analysis, supported by quantum chemical calculations, has revealed that while cisplatin attack is mainly directed to the sulfur atom of Met, transplatin shows a more balanced partition between sulfur and nitrogen binding. Among the vibrational signatures characterizing cis-[PtCl(NH3)2Met]+ and trans-[PtCl(NH3)2Met]+ complexes, the asymmetric NH2 stretching of the α-amino group of the amino acid at ca. 3440 cm−1 is peculiar and diagnostic of S-platination. IRMPD kinetics evaluated at this frequency support the prevailing S-attack by cisplatin while approximately a 1 : 2 ratio of S- versus N-coordination is observed by transplatin, to be possibly related to the trans effect at the platinum center.

Zn-salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of IRMPD spectroscopy experiments and quantum chemical calculations, the structure of the host-guest complexes formed by two efficient Zn-salophen receptors and dihydrogen phosphate or adenosine 5′-monophosphate (AMP) anions. In the host-guest complexes the phosphate group is bound with a Zn O(phosphate) bond. In addition, a hydrogen bond can be formed between the PO H group and one of the oxygen atoms of the salophen structure. The complexes with AMP anions are endowed with a hydrogen bonded coordination motif together with a weaker π⋯π interaction. It is thus confirmed that the marked changes of the spectroscopic emission properties of Zn-salophen when complexed with AMP can be associated with the existence of π⋯π stacking interactions between the salophen aromatic rings and those of the adenosine nucleobase.

The conformational landscape of (S)-1-(4-chlorophenyl)ethanol, its monohydrated complex, and its diastereomeric adducts with R- and S-butan-2-ol, have been investigated by resonant two-photon ionization (R2PI) spectroscopy coupled with time-of-flight mass spectrometry. Theoretical calculations at the D-B3LYP/6-31++G** level of theory have been performed to assist in the interpretation of the spectra and in the assignment of the structures. The R2PI spectra and the predicted structures have been compared with those obtained on the analogous non-halogenated and fluorinated systems, i.e., (R)-1-phenylethanol and (S)-1-(4-fluorophenyl)ethanol, respectively. It appears that the presence of chlorine atom in the para position of the aromatic ring does not influence the overall geometry of bare molecule and its complexes with respect to the non-halogenated analogous systems. Anyway, it affects the electron density in the pi system, and in turn the strength of OH···pi and CH···pi interactions. A spectral chiral discrimination is evident from the R2PI spectra of the diastereomeric adducts of (S)-1-(4-chlorophenyl)ethanol with the two enantiomers of butan-2-ol.

Here, we report the observation of electron transfer mediated decay (ETMD) involving Mg clusters embedded in helium nanodroplets which is initiated by the ionization of helium followed by removal of two electrons from the Mg clusters of which one is transferred to the He environment neutralizing it while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. The photoelectron spectrum reveals a low energy ETMD peak. For Mg clusters larger than 5 atoms we observe stable doubly-ionized clusters. We argue that ETMD provides a new pathway to the formation of doubly-ionized cold species., 5 pages submitted to Phys. Rev. Lett

3rd SPIE Conference on Advances in X-Ray Free-Electron Lasers Instrumentation, Prague, CZECH REPUBLIC, APR 13-16, 2015; International audience; Magnetization control without applying magnetic fields has potential for applications in sensors and devices. In Fe/MnAs/GaAs(001), the Fe magnetization can be modified by acting on the MnAs microstructure via temperature control, without applying external magnetic fields. Here we use an optical laser pulse to vary the local temperature and an x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics in a time-resolved resonant scattering experiment, both pulses having similar to 100 fs duration. Modifications of the MnAs microstructure take place within a few ps, followed by a slower dynamics driven by thermal diffusion. We show that a single optical laser pulse can reverse the Fe magnetization locally, the process being driven not by the fast modifications of the MnAs structure, but rather by its slower return to equilibrium.

International audience; The experimental set-up for time-resolved studies of ultra-fast photo-induced structural dynamics at the Synchrotron SOLEIL is based on a general pump-probe scheme that has been developed and implemented on the CRISTAL hard X-ray diffraction beamline [1,2]. In a so-called pump-probe cycle, the sample is excited with an ultra-short laser pulse of ≈40 fs duration (the pump), and induced changes in its atomic structure are studied by measuring, with a precisely controlled delay, a diffraction pattern from a single pulse of synchrotron radiation (the probe) with a 2-D pixel detector. An improvement to the classical scheme is proposed, where the sample's response is probed at two different delays after each laser excitation. The first measurement at short delays allows studying the photo-induced dynamics. The second one is a reference measurement taken after sample's relaxation, which permits detection of drifts in the experimental conditions (e.g. beam misalignment, sample degradation). A hybrid pixel detector with a very fast readout time, a high dynamic range and extended linearity was tested to achieve the experiment objectives. In this paper, the first results obtained with the UFXC32k single photon counting detector are presented.

Thin film magnetization reversal without applying external fields is an attractive perspective for applications in sensors and devices. One way to accomplish it is by fine-tuning the microstructure of a magnetic substrate via temperature control, as in the case of a thin Fe layer deposited on a $\mathrm{MnAs}/\mathrm{GaAs}(001)$ template. This work reports a time-resolved resonant scattering study exploring the magnetic and structural properties of the $\mathrm{Fe}/\mathrm{MnAs}$ system, using a 100 fs optical laser pulse to trigger local temperature variations and a 100 fs x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics. The experiment provides direct evidence that a single optical laser pulse can reverse the Fe magnetization locally. It reveals that the time scale of the magnetization reversal is slower than that of the MnAs structural transformations triggered by the optical pulse, which take place after a few picoseconds already.

The vibrational features and molecular structures of complexes formed by a series of uranyl-salophen receptors with simple anions, such as Cl(-) , H(-) , and HCOO(-) , have been investigated in the gas phase. Spectra of the anionic complexes were studied in the $\tilde \nu $=800-1800 cm(-1) range by mass-selective infrared multiple photon dissociation (IRMPD) spectroscopy with a continuously tunable free-electron laser. The gas-phase decarboxylation of the formate adducts produces uranyl-salophen monohydride anions, which have been characterized for the first time and reveal a strong UH bond, the nature of which has been elucidated theoretically. The spectra are in excellent agreement with the results obtained from high-quality ab initio calculations, which provided the structure and binding features of the anion-receptor complexes.

We present the main features of CITIUS, a new light source for ultrafast science, generating tunable, intense, femtosecond pulses in the spectral range from IR to XUV. The XUV pulses (about 105-108 photons/pulse in the range 14-80 eV) are produced by laser-induced high-order harmonic generation in gas. This radiation is monochromatized by a time-preserving monochromator, allowing also to work with high-resolution andwidth selection. The tunable IR-UV pulses (1012--1015 photons/pulse in the range 0.4-5.6 eV) are generated by an optical parametric amplifier, which is driven by a fraction of the same laser pulse that enerates high order harmonics. The IR-UV and XUV pulses follow dierent optical paths and are eventually recombined on the ample for pump-probe experiments. The new light source will become the fulcrum of a new center located at the University of Nova Gorica, active in a wide range of scientific fields, including materials science, catalysis, biochemistry and magnetism. We also present the results of two pump-probe experiments: with the first one, we fully characterized the temporal duration of harmonic pulses in the time-preserving configuration; with the second one, we demonstrated the possibility of using CITIUS for selective investigation of the ultra-fast dynamics of dierent elements in a magnetic compound.

The kinetic-energy distribution of interatomic and -molecular Coulombic decay (ICD) electrons emitted following photoionization of $2s$ electrons from Ne atoms in NeAr dimers has been measured in a synchrotron radiation experiment with a velocity-map-imaging photoelectron-photoion-coincidence spectrometer. The position of the peak of the experimental distribution agrees well with calculations. The broadening of the distribution to high energies with respect to calculations of the ICD spectrum of the NeAr $v=0$ ground state is explained by the contribution to the spectrum due to the population in the excited vibrational states $v=1$ and $v=2$ of the electron ground state. On the other hand, the broadening on the low-energy side of the measured distribution may be explained by the dimer contracting in the intermediate state before ICD occurs, electrons coming from the ICD to spin-orbit split excited ion states, or a combination of these effects.

The vibrational spectra of ciprofloxacin complexes with monovalent (Li +, Na+, K+, Ag+) and polyvalent (Mg2+, Al3+) metal ions are recorded in the range 1000-1900 cm-1 by means of infrared multiple-photon dissociation (IRMPD) spectroscopy. The IRMPD spectra are analyzed and interpreted in the light of density functional theory (DFT)-based quantum chemical calculations in order to identify the possible structures present under our experimental conditions. For each metal-ciprofloxacin complex, four isomers are predicted, considering different chelation patterns. A good agreement is found between the measured IRMPD spectrum and the calculated absorption spectrum of the most stable isomer for each complex. Metal ion size and charge are found to drive the competition among the different coordination motifs: small size and high charge density metal ions prefer to coordinate the quinolone between the two carbonyl oxygen atoms, whereas large-size metal ions prefer the carboxylate group as a coordination site. In the latter case, an intramolecular hydrogen bond compensates the weaker interaction established by these cations. The role of the metal cation on the stabilization of ionic and nonionic structures of ciprofloxacin is also investigated. It is found that large-size metal ions preferentially stabilize charge separated motifs and that the increase of metal ion charge has a stabilizing effect on the zwitterionic form of ciprofloxacin. © 2012 American Chemical Society.

A computational and vibrational spectroscopic study of the aqua complexes obtained by hydrolysis of cis- and trans-diamminedichloroplatinum(II) is reported. Electrospray ionization has allowed cis-...

The molecular diastereomeric complexes between R-1-phenyl-1-ethanol, S-1-(4-fluorophenyl)ethanol and S-1-(2-fluorophenyl)ethanol and R and S-butan-2-ol, isolated under molecular beam conditions in the gas phase, have been investigated by mass-selective resonant two-photon ionization (R2PI) and infrared depleted R2PI (IR-R2PI). The comparison of the three systems allowed us to highlight the significance of specific intermolecular interactions in the chiral discrimination process. The interpretation of the results is based on theoretical predictions mainly at the D-B3LYP/6-31++G** level of theory. The homo and heterochiral complexes are endowed with fine differences in intermolecular interactions, namely strong OH⋯O, and weaker CH⋯π, OH⋯π, CH⋯F as well as repulsive interactions. The presence of a fluorine atom in the para position of the aromatic ring does not influence the overall geometry of the complex whilst it affects the electron density in the π system and the strength of CH⋯π and OH⋯π interactions. The role and the importance of CH⋯F intermolecular interactions are evident in the complexes with fluorine substitution in the ortho position. While the ortho hetero complex is structurally analogous to the hetero para and non-fluorinated structures, butan-2-ol in the ortho homo adduct adopts a different conformation in order to establish a CH⋯F intermolecular interaction. © 2013 the Owner Societies.

The vibrational spectrum of isolated protonated ciprofloxacin was recorded in the range 1100–2000 cm −1 by means of infrared multiple photon dissociation (IRMPD) spectroscopy. The spectrum was obtained by electrospraying a methanol solution of ciprofloxacin in a Paul ion trap, coupled to the tunable IR radiation of a free electron laser. This spectroscopic study has been complemented by quantum chemical calculations at the DFT and MP2 levels of theory to identify the possible structures present under our experimental conditions. Several low-energy isomers with protonation occurring at the piperazinyl amino group and at the carbonyl group are predicted in the energy range 0–84 kJ mol −1 . A good agreement between the measured IRMPD spectrum and the calculated absorption spectrum is observed for the isomer protonated at the piperazinyl amino group. This isomer is calculated at MP2 level of theory to lie about 76 kJ/mol above the most stable isomer which is protonated at the quinone carbonyl group. This discrepancy can be rationalized by assuming that the protonation at the piperazinyl amino group, typical of the zwitterionic form that is found in protic solvents, is retained in the ESI process. The vibrational bands observed in the IRMPD spectrum are assigned to normal modes of the isomer protonated at the piperazinyl amino group, with deviations of less than 20 cm −1 between measured and calculated frequencies.

Diastereomeric adducts between (S)-1-(4-fluorophenyl)-ethanol and R and S 2-butanol, formed by supersonic expansion, have been investigated by means of a combination of mass selected resonant two-photon ionization-spectroscopy and infrared depletion spectroscopy. Chiral recognition is evidenced by the specific spectroscopic signatures of the S(1)← S(0) electronic transition as well as different frequencies and intensities of the OH stretch vibrational mode in the ground state. D-DFT calculations have been performed to assist in the analysis of the spectra and the determination of the structures. The homochiral and heterochiral complexes show slight structural differences, in particular in the interaction of the alkyl groups of 2-butanol with the aromatic ring. The experimental results show that the homochiral [FE(S)·B(S)] complex is more stable than the heterochiral [FE(S)·B(R)] diastereomer in both the ground and excited states. The binding energy difference has been evaluated to be greater than 0.60 kcal mol(-1).

We present the design and characterization of a double-configuration grating monochromator for the spectral selection of extreme-ultraviolet ultrafast pulses. Two grating geometries are joined in an instrument with two interchangeable diffracting stages, both used at grazing incidence: one with the gratings in the off-plane mount (OPM), the other in the classical diffraction mount (CDM). The use of two stages gives great flexibility: the OPM stage is used for sub-50 fs time response and low spectral resolution, while the CDM stage is for 100-200 fs time response and high spectral resolution. The monochromator spectral and temporal performances have been experimentally demonstrated on a high-order laser-harmonics beam line.