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The absolute densities of O and O 3 in the effluent of a kINPen, an atmospheric pressure plasma jet, are determined by molecular beam mass spectrometry. A nitrogen gas curtain surrounding the effluent provides a stable environment and prevents interactions with the ambient air. Both He and Ar were used as feed gas with admixtures of O 2 up to 1%. Measurements are performed at discharge voltages from 1600 to 3000 V pp and at distances from 5.5 to 10.5 mm from the nozzle of the gas shielding device to the orifice of the mass spectrometer. The measured O atom densities are in the order of 1 × 10 14 cm - 3 to 2 × 10 15 cm - 3 , whereas the O 3 molecule densities are in the order of 1 × 10 14 cm - 3 to 5 × 10 14 cm - 3 , respectively, when operated in argon the plasma generates higher densities of reactive species. Additionally, a novel molecular beam chopper design with linear movement has been successfully tested in the mass spectromerty setup as an alternative to a rotating chopper. [ABSTRACT FROM AUTHOR]

A detailed description of a custom-made gas aggregation cluster source is given as well as of its coupling to permanent molecular beam end-stations of the beamlines DESIRS and PLEIADES at the French national facility synchrotron SOLEIL. Using (hydrated) hypoxanthine clusters as a case study, the production of clusters with different source parameters is discussed based on Vacuum Ultra-Violet (VUV) mass spectrometry. The ability of the cluster source to perform photoelectron spectroscopy is illustrated by photoelectron spectra obtained for valence and core shells. [ABSTRACT FROM AUTHOR]

We have produced a cryogenic buffer-gas cooled beam of the diatomic molecular radical CH (methylidyne). This molecule is of interest for studying cold chemical reactions and fundamental physics measurements. Its light mass and ground-state structure make it a promising candidate for electrostatic guiding and Stark deceleration, which allows for control over its kinetic energy. This control can facilitate studies of reactions with tuneable collision energies and trapping for precise spectroscopic studies. Here, we have demonstrated electrostatic guiding of CH with fluxes up to 109 molecules per steradian per pulse. [ABSTRACT FROM AUTHOR]

Experiments that probe the fundamental properties of endohedral fullerenes often require the preparation of molecular beams or thin films of the neutral molecules. It is challenging to cleanly sublime this class of molecules without producing some thermal degradation. We report combined gas phase and scanning tunnelling microscopy studies that probe the thermal decay of commercial [Li+C60]PF6- in a quartz ampoule and provide treatment conditions that will allow the sublimation of intact, neutral Li@C60 accompanied by a well-characterised component of neutral C60. The decay of the material at appropriate temperatures can be modelled with the assumption of a second order decay process in the oven yielding Arrhenius parameters that can predict the ratio of Li@C60 to C60 in the sublimed material. [ABSTRACT FROM AUTHOR]

This paper is an overview of our recent experimental investigations of the RgI van der Waals complexes, Rg = He, Ar, Kr, performed by means of laser induced fluorescence spectroscopy, optical-optical double resonance and supersonic molecular beam techniques. Spectroscopic parameters of these complexes in the E0 ion-pair state, such as binding energies and several spectroscopic constants, have been determined. Most likely, the potential energy surfaces of the all RgI( E) complexes under study present T-shaped minima. Vibrational and electronic predissociations of the RgI( E) complexes were analyzed. Relative contributions of the different electronic predissociation channels and vibrational distributions of the decay products were determined. Possible mechanisms of the complexes decay are suggested and discussed. [ABSTRACT FROM AUTHOR]

Using nonadiabatic and adiabatic classical trajectory methods, we investigate nonadiabatic effects in collision of H + with H 2 for the collision energy in the range of 0.01 and 3.0 eV. Comparison with adiabatic calculations are used to give insight on the nonadiabatic charge transfer process. [ABSTRACT FROM AUTHOR]

In a newly built molecular beam apparatus we have measured permanent electric dipole moments of the B Π and X Σ states of NaK to test the vibrational dependence of the dipole moment function as predicted by ab initio calculations by Aymar and Dulieu [J. Chem. Phys. 122, 204302 (2005)]. Four vibrational bands were studied, the dipole moment for the B Π decreases from 2.73(2) D for v = 3 to 1.99(2) D for v = 13. The vibrational dependence shows a fairly good agreement with theory, but the absolute values are lower than those from the calculation by 13%. The ground state dipole moment of 2.72(6) confirms the earlier result by Wormsbecher et al. [J. Chem. Phys. 74, 6983 (1981)]. [ABSTRACT FROM AUTHOR]

A molecular beam interference model is presented based on a two-state interaction between a polar molecule and a resonant RF field as it occurs in the so-called C-field of a typical molecular beam electric resonant spectrometer. The treatment shows the onset of interferences in the beam transmission spectra as well as in its transverse profile. It is demonstrated how the molecular interferences are originated by the wavefunction phase shift introduced by the resonant RF field. Furthermore it is shown that for a given beam velocity and oscillating field frequency the fringes’ visibility depends on the strength of the RF field, i.e. the Rabi frequency, in the transmission spectra. Likewise the presence of a RF field gradient in the perpendicular beam direction gives rise to a peak structure in the transverse beam profile. The theoretical model was applied to simulate a variety of beam transmission spectra under resonant conditions as well as some experimental data already published by our group showing a satisfactory agreement between experimental and simulated data. Finally, the potentiality of this internal state molecular interferometer to carry out studies in matter-wave interferometry is remarked. [ABSTRACT FROM AUTHOR]

Rovibrational excited hydrogen molecule plays an important role for the production of H- ions. The correlation between H- ion density and rovibrational distribution of H2 molecules has been investigated in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry and molecular beam mass spectrometry. The relative vibrational distribution of molecular hydrogen in the electronic ground state has been determined by the best fitting to the Fulcher-α band emission lines. It is shown that the ratio of the Q(0-0)(1) to Q(1-1)(1) line is very suitable and simple for the diagnosis of vibrational temperature in the range of 1500 to 7500 K. At certain discharge conditions (ac 40 kHz, 14 kV), the vibrational temperature decreases from 3600 to 2400 K as the pressure increases from 100 to 200 Pa and the negative ions density near the ground electrode also decreases as the pressure increases. Both the hydrogen ions density and the vibrational temperature increase with the increasing of discharge voltage. It is found that the evolution of negative atomic hydrogen ions density greatly depends on the vibrational temperature. [ABSTRACT FROM AUTHOR]

Integral cross sections and pressure broadening coefficients have been measured for the acetylene — neon system by a molecular beam scattering technique and by high infrared resolution spectroscopy, respectively. We have performed quantal calculations using an ab-initio potential energy surface (PES) [J. Chem. Phys. 109, 8968 (1998)]. Results are found to be in good agreement with both measured integral cross sections and pressure broadening coefficients for the two temperatures investigated (173 and 298 K). We have also derived a semi-empirical PES parameterized using an atom-bond pairwise additive scheme. This PES shows an isotropic component in agreement with the ab-initio calculation, reproduces the scattering data but it only leads to a reasonable agreement for the pressure broadening coefficients. [ABSTRACT FROM AUTHOR]

Absolute transition frequencies of the b 3Π(0u +) - X 1Σg + system of K2 were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K2 molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K2 molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined. [ABSTRACT FROM AUTHOR]

Absolute transition frequencies of the b 3Π(0u +) - X 1Σg + system of K2 were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K2 molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K2 molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined. [ABSTRACT FROM AUTHOR]

The full three-dimensional velocity distributions of decelerated and accelerated particles in a Stark decelerator for Rydberg atoms and molecules have been measured. In the experiment, argon atoms in a supersonic beam are excited to low-field and high-field seeking Stark states with principal quantum number in the range n=15 to 25 and are decelerated in a 3 mm long decelerator consisting of four electrodes on which time-dependent voltages are applied. The time dependence of the resulting inhomogeneous electric field is chosen such that the decelerating force acting on the high-field seeking states is maximized at each point along the trajectories. The three-dimensional velocity distribution of the atoms before and after the deceleration is determined by measuring times of flight and two-dimensional images of the atomic cloud on the detector. Under optimal deceleration conditions, the decrease in kinetic energy in the longitudinal dimension amounts to 1.0×10-21 J and the increase in mean kinetic energy in the transverse dimensions is only 1.0×10-23 J. The corresponding temperatures of 100 mK and 300 mK in the two transverse dimensions are sufficiently low that trapping can be envisaged. The possibility of focusing a Rydberg atom beam is demonstrated experimentally. [ABSTRACT FROM AUTHOR]

In our previous work we investigated electronically non-adiabatic effects in $\rm Cl~(^{2}P_{3/2,1/2})+D_{2}$ using crossed molecular beam scattering coupled with velocity mapped ion imaging. The prior experiments placed limits on the cross-section for electronically non-adiabatic spin-orbit excitation $\rm Cl~(^{2}P_{3/2})+D_{2} \to Cl^*~(^{2}P_{1/2})+D_{2}$ and electronically non-adiabatic spin-orbit quenching $\rm Cl^*~(^{2}P_{1/2})+D_{2}\to Cl~(^{2}P_{3/2})+D_{2}$ . In the present work, we investigate electronically non-adiabatic spin-orbit quenching for $\rm Cl^*~(^{2}P_{1/2})+H_{2}$ which is the required first step for the reaction of Cl* to produce ground state HCl+H products. In these experiments we collide Cl (2P) with H2 at a series of fixed collision energies using a crossed molecular beam machine with velocity mapped ion imaging detection. Through an analysis of our ion images, we determine the fraction of electronically adiabatic scattering in Cl* +H2, which allows us to place limits on the cross-section for electronically non-adiabatic scattering or quenching. We determine the following quenching cross-sections σ quench(2.1 kcal/mol) = 26 ± 21 Å2, σ quench(4.0 kcal/mol) = 21 ± 49 Å2, and σ quench(5.6 kcal/mol) = 14 ± 41 Å2. [ABSTRACT FROM AUTHOR]

The experimental apparatus for investigating the gas-surface interaction has been newly developed. The coherent length of the helium, the energy resolution and the angular spread of the beam in the apparatus were established as ω= 16 nm, $\Delta E/E = 2.4{\%}$ and Δθ= 0.5○, respectively, through the measurements of the time-of-flight of He beam and of the angular intensity distributions of He scattered from LiF(001). The angular intensity distributions of Ar, N2 and CO scattered from the LiF(001) surface along the [100] azimuthal direction were then measured as a function of incident translational energy. The effects of the molecular structural anisotropy and center-of-mass position on the gas-surface inelastic collision at the corrugated surface are discussed with predictions based on a recently developed simple classical theory of the ellipsoid-washboard model. [ABSTRACT FROM AUTHOR]

Deflection of a cold supersonic NO beam seeded in He has been observed when these molecules interact with both static and a resonant oscillating electric field. The NO beam splits into two beams each one deflecting about 0.5° towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the NO molecule is 1515 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the NO dipole moment and the employed RF field gradient. This phenomenon suggests the possibility of a significant translational motion perpendicular to the beam axis, which is induced by the resonant RF electric field on the cold and high-density supersonic beam. [ABSTRACT FROM AUTHOR]

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X2Π-A2Σ+ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO+ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T. [ABSTRACT FROM AUTHOR]

We present a simple analytic approximation for evaluating the ensemble-averaged orientation or alignment of a beam of molecules subjected to a strong static or radiative field. This approximation is based on the eigenproperties which polar or polarizable molecules exhibit in the strong-field, harmonic-librator limit, and on the Boltzmann statistics of the free rotor states which adiabatically correlate with the harmonic librator states. For either the permanent or induced dipole case, the resultant formula involves just two dimensionless parameters which characterize the strength of the molecule-field interaction and the rotational temperature. The net polarization of a molecular beam thus obtained is shown to be in an excellent agreement with the exact values computed numerically from first principles. The validity range of the approximation includes the large-interaction, high temperature regions of the parameter space where first-principle calculations are onerous. [ABSTRACT FROM AUTHOR]

The scattering of a hyperthermal Xe from a graphite (0001) surface has been studied using a molecular beam-surface scattering technique and molecular dynamics (MD) simulations. The angular and velocity distributions of scattered Xe atoms were measured at incidence energies from 0.45 to 3.5 eV, three incidence angles of 15°, 35° and 60° and the surface temperatures of 300 K and 550 K. The observed time-of-flight spectra exhibit a sharp velocity distribution with only one velocity component, which is ascribed to the direct inelastic scattering process. The angle-resolved energy ratios of the mean final translational energy over the mean incidence energy Ef/Ei agree well with those predicted based on the assumption of the conservation of the momentum parallel to the surface. The Hard-Cube model, where the mass of the cube is approximately 310 u, has reproduced the angle-resolved flux distributions of scattered Xe atoms. In the Hard-Cube model almost 80% of the normal component of the incidence translational energy is found to be lost in collision. The MD simulations reproduce well the experimental results by using the Brenner potential for intralayer C atoms and a Lennard-Jones potential for interlayer C–C pair interactions. [ABSTRACT FROM AUTHOR]

We report a study on the oxidation process induced by a hyperthermal oxygen molecular beam (HOMB) on Cu(110) using X-ray photoemission spectroscopy in conjunction with a synchrotron radiation source. The oxidation process induced by energetic O2 beams on Cu(110), depending on the azimuthal angle of incidence, suggests that the –Cu–O– added row structure has a role in inhibiting adsorption as a steric obstacle for incident O2 molecules. [ABSTRACT FROM AUTHOR]

In the mid-seventies, Case and Herschbach argued that for complex-forming three-atom reactions governed by long-range forces and performed in supersonic molecular beam experiments, vectorial properties are determined by a single parameter Λ' = 〈L'/(L' + j')〉, L' and j' being respectively the moduli of the orbital and rotational angular momenta of the products. A simple mathematical relation between vectorial properties and Λ' was then proposed. However, Λ' must be determined beforehand by phase space theory calculations. Besides, we have recently shown that scalar properties are mainly controled by two factors ρ'1 and ρ'2 respectively called angular excitation and diatomic inertial contribution. We show here that these factors control also vectorial properties. Moreover, the way they control them is summarized in a set of four figures. The advantage of our method is that ρ'1 and ρ'2 are related to the mechanical parameters of the reaction by very simple formulas, contrary to Λ'. Last by not least, our parameters appear to be mostly independent, so that vectorial properties cannot be said to strictly depend on Λ'. Nevertheless, it turns out that the rule proposed by Case and Herschbach is reasonable in many realistic situations. [ABSTRACT FROM AUTHOR]

Low energy electron attachment to the fullerene molecule (C60) and its temperature dependence are studied in a crossed electron beam–molecular beam experiment. We observe the strongest relative signal of C60 anion near 0 eV electron energy with respect to higher energy resonant peaks confirming the contribution of s-wave capture to the electron attachment process and hence the absence of threshold behavior or activation barrier near zero electron energy. While we find no temperature dependence for the cross-section near zero energy, we observe a reduction in the cross-sections at higher electron energies as the temperature is increased, indicating a decrease in lifetime of the resonances at higher energies with increase in temperature. [ABSTRACT FROM AUTHOR]

Dissociative electron attachment (DEA) to CHCl2Br has been studied in a crossed electron/molecular beams experiment in the electron energy range between 0 and 8 eV and in the gas temperature range from 321 to 478 K. The two negative fragment ions Cl- and Br- are formed from a prominent low energy resonant feature close to zero eV and at comparatively weaker resonances at about 0.38 eV, 2.2 eV and 5.5 eV. In contrast to swarm experiments [7], the bihalogen ion Cl2- was not detected in our experiment. The absolute partial cross-sections for Br- and Cl- reaction channels have been estimated. We find that in the low electron energy range (≈0 eV) the overall DEA cross-section as well as the partial DEA cross-section for Br- formation slightly decrease with increasing gas temperature whilst the partial cross-section for the Cl- channel is temperature independent. [ABSTRACT FROM AUTHOR]

Quantum calculations and experiments with molecular beams have been carried out for the Formic Acid dimeric structures colliding with a beam of slow (<20 eV) electrons. The corresponding computed S-matrix poles, seen as signatures for the formation of transient negative ions, allow us to assign the resonances to specific doorway states which are suggested to be responsible for the fragmentation patterns observed in the present experiments and in earlier measurements carried out both in molecular beams and with films of formic acid. We further show the computed behaviour of partial cross-sections and partial eigenphase sums for the dominant symmetry components. [ABSTRACT FROM AUTHOR]

Low energy electron attachment to the fullerene molecule (C60) and its temperature dependence are studied in a crossed electron beam–molecular beam experiment. We observe the strongest relative signal of C60 anion near 0 eV electron energy with respect to higher energy resonant peaks confirming the contribution of s-wave capture to the electron attachment process and hence the absence of threshold behavior or activation barrier near zero electron energy. While we find no temperature dependence for the cross-section near zero energy, we observe a reduction in the cross-sections at higher electron energies as the temperature is increased, indicating a decrease in lifetime of the resonances at higher energies with increase in temperature. [ABSTRACT FROM AUTHOR]

Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum ofusing a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions inin thestate (around 1.43 GHz) are induced in a microwave region, andmolecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz. [ABSTRACT FROM AUTHOR]

We report the cooling of nitric oxide molecules in a single collision between an argon atom and an NO molecule at collision energies ofkJ/mol andkJ/mol in a crossed molecular beam apparatus. We have produced in significant numbers (~108 molecules cm-3 per quantum state) translationally cold NO(,v’ = 0,j’ = 7.5) molecules in a specific quantum state with an upper-limit laboratory-frame rms velocity ofm/s, corresponding to a temperature ofmK. The translational cooling results from the kinematic collapse of the velocity distribution of the NO molecules after collision. Increasing the collision energy by increasing the velocity of the argon atoms, as we do here, does shift the scattering angle at which the cold molecules appear, but does not result in an experimentally measurable change in the velocity spread of the cold NO. This is entirely consistent with our analysis of the kinematics of the scattering which predicts that the velocity spread will actually decrease with increasing argon atom velocity. [ABSTRACT FROM AUTHOR]

NH radicals from a molecular beam are cooled using a novel beam-loaded buffer gas method. The radicals are produced in a glow discharge beam source and injected into cryogenic helium gas. Up to 1012 molecules in their ground electronic, vibrational, and rotational state are detected in the buffer gas and translational temperatures under 6 K are achieved. The cooling method presented is general and can be applied to any molecules in a molecular beam. [ABSTRACT FROM AUTHOR]

The slowing down of Co10Ag191 and Co285Ag301 nanoclusters on a Ag (100) surface is studied at the atomic scale by means of classical Molecular Dynamics simulations. The slowing down energy, 0.25 to 1.5 eV/atom, is characteristic of low energy cluster beam deposition and aerosol focused beam techniques. The two clusters differentiate by their size, stoechiometry and structure. While Co forms one or several groups just beneath the cluster surface in Co10Ag191, Co285Ag301 displays a core-shell structure where Ag forms one complete monolayer around the Co core. As a consequence of the impact, the smallest cluster undergoes deep reorganization and becomes fully epitaxial with the substrate. The larger one only undergoes partial accommodation and partially retains the memory of its initial morphology. For both, after impact, the Co forms one group covered by Ag. The substrate damage is significant and depends on the slowing down energy. It results in a Ag step surrounding the cluster which may be more than one atomic layers high and isolated add-atoms or small monolayer islands apart from the step. The latter originate from the cluster and the former from the substrate. Further details in the consequences of the impact are given, concerning the cluster penetration, its deformation and lattice distortions, with emphasis on the cluster size and stoechiometry. [ABSTRACT FROM AUTHOR]

Recently, different approaches have been implemented to detect single molecules with an optical dipole out of the sample plane. Principles to solve this problem of general interest have been laid but no detailed analysis has been performed to date. This paper is devoted to a quantitative analysis of the dipole orientation of out of plane molecules that we have detected by amplitude and phase masking of the input beam. The accuracy of the orientation is discussed. [ABSTRACT FROM AUTHOR]

Diffraction of molecular beams of CH3F, CHF3, and metastable He* and Ne* from a 100-nm-period micro-fabricated transmission grating has been observed. Due to the finite velocity spread and the corresponding temporal coherence of the molecular beams, diffraction peaks of only the first few orders are resolved in total-intensity measurements, while higher order peaks are increasingly broadened and smeared-out. Combining time-of-flight (TOF) measurements with angular scans has allowed to observe TOF-resolved diffraction data which yield full resolution of all detected diffraction peaks. Here, this method has been applied to investigate atom/molecule-surface interactions. In general, it can be used to observe resolved diffraction patterns of a wide range of atomic and molecular beams whose broad velocity distributions prevent peak-resolution in conventional total-intensity measurements. [ABSTRACT FROM AUTHOR]

We investigate the influence of a laser field, which is near-resonant to the atomic sodium 3²P1/2 → 3²D3/2 transition, on the last bound levels of the A¹Σu+ state in Na2. In a molecular beam experiment level shifts up to ≈ 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3²S1/2 and a 3²P1/2-atom the scattering phase is altered by more than π. The observed effects are interpreted as light induced couplings of the A¹Σu+ state, which correlates to the 3s1/2 + 3p1/2 asymptote, to the 4¹Σg+ and 2¹Πg states at the 3s1/2 + 3d3/2 asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well. [ABSTRACT FROM AUTHOR]

We report on a novel phenomenon observed during the passage of a pulsed NO beam seeded in He through a combined homogeneous, static electric and RF field, denoted as C-field in a standard molecular beam electric resonance (MBER) experiment. Although we refrain from the state selective A- and B-fields, which are considered crucial for a MBER experiment, the transmitted intensity exhibits as a function of the RF frequency conspicuous dips at resonance frequencies that depend strictly linearly on the static field strength E0. Their spectral width is by a factor of 4 smaller than the time of flight broadening. Both, the resonance frequencies and their linear field dependence can be precisely predicted applying a simple expression for the Stark effect to a ΔM = ±1 transition of a single rotational state (J = 3/2) of the electronic ground state ²Π1/2. However, this formula is valid only in the high field limit (E0 > 1000 kV/m) while the employed field (E0 1.47 kV/m) was in the extreme low field domain where the large A type doubling and hyperfine coupling lead to a purely quadratic Stark effect. We assume that the phenomenon is due to a yet unknown collective rather than to an isolated particle process. [ABSTRACT FROM AUTHOR]

We investigate the influence of a laser field, which is near-resonant to the atomic sodium 3²P1/2 → 3²D3/2 transition, on the last bound levels of the A¹Σu+ state in Na2. In a molecular beam experiment level shifts up to ≈ 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3²S1/2 and a 3²P1/2-atom the scattering phase is altered by more than π. The observed effects are interpreted as light induced couplings of the A¹Σu+ state, which correlates to the 3s1/2 + 3p1/2 asymptote, to the 4¹Σg+ and 2¹Πg states at the 3s1/2 + 3d3/2 asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well. [ABSTRACT FROM AUTHOR]

We report on the first observation of the outer well of the (6)¹ Σg+ state of Na2 molecule. The levels are populated in a molecular beam experiment with a three step laser excitation. The fact that these levels predissociate allows an almost background free detection by the appearance of atomic fluorescence. With this method almost all vibrational levels of the outer well are observed. The corresponding predissociation line widths show an oscillating behaviour. The theoretical description of the predissociation is presented in the framework of mapped Fourier grid Flamiltonian representation with optical potential, involving two coupled electronic states. Combining the spectroscopic information on energy positions and predissociation widths, a Rydberg-Klein-Rees potential curve is given for the outer well. Such a state could offer a reliable path for photoassociation of cold Na atoms and formation of ultracold Na2 molecules. [ABSTRACT FROM AUTHOR]

Using realistic pair potentials, we investigate the structures of mixed clusters of argon and nitrogen in order to interpret the experimental electron diffraction patterns reported by the Torchet group. Simulations of small clusters indicate that argon tends to segregate at the center of the clusters. For larger clusters, in the range of 50 to 200 molecules, MC methods have been used to simulate structures that are likely to be generated in the molecular beam. By comparing predicted electron diffraction patterns with those recorded in the experiments, our models allow us to estimate the average size and composition of the mixed clusters for a given set of experimental conditions (nozzle stagnation pressure and Ar partial pressure). [ABSTRACT FROM AUTHOR]

The absorption spectrum of NaAr has been investigated with high resolution using a supersonic beam of molecules and a tunable dye laser. About 3 300 absorption lines due to the transition A 2Π ← X and B 2Π ← X have been observed. In addition, we observed the spectral distribution of the fluorescence for a particular absorption line. From all experimental data the X 2Π+ interaction potential has been deduced in a fully quantum-mechanical method of approach. The potential is given in terms of an analytical Hartree-Fock-Dispersion function. For the equilibrium parameters of the X state we get Re = 5.01(1) Å and De = 41.6(2) cm-1. [ABSTRACT FROM AUTHOR]

Carbon nanotube properties can be modified by ion irradiation; therefore it is important to know the manner in which ions deposit energy (how much and where) in the nanotubes. In this work, we have studied, experimentally and with a simulation code, the irradiation of multi-walled carbon nanotubes (MWCNT), supported on a holey amorphous carbon (a-C) substrate, with low energy (2–10 keV/u) H+ and H2+ molecular beams, impinging perpendicularly to the MWCNT axis. The energy distribution of protons traversing the nanotubes (either from the H+ beam or dissociated from the H2+ beam) was measured by the transmission technique in the forward direction. Two well-differentiated peaks appear in the experimental energy-loss distribution of the fragments dissociated from the molecular H2+ beam, in correspondence to the ones detected with the proton beam. One is the low-energy loss peak (LELP), which has a symmetric width; the other is the high-energy loss peak (HELP), which shows an asymmetric broadening towards larger energy loss than the corresponding proton energy distribution. A semi-classical simulation, accounting for the main interaction processes (both elastic and inelastic), of the proton trajectories through the nanotube and the supporting substrate has been done, in order to elucidate the origin of these structures in the energy spectra. Regarding the H+ energy spectrum, the LELP corresponds to projectiles that travel in quasi-channelling motion through the most outer walls of the nanotubes and then pass through the substrate holes, whereas the HELP results mostly from projectiles traversing only the a-C substrate, with the asymmetry broadening being due to a minor contribution of those protons that cross the a-C substrate after exiting the nanotube. The broadening of the peaks corresponding to dissociated fragments, with respect to that of the isolated protons, is the result of vicinage effects between the fragments, when travelling in quasi-channelling conditions through the outer layers of the nanotube, and Coulomb explosion just after exiting the target. The excellent agreement between the measured and the simulated energy spectra of the H+ beam validates our simulation code in order to predict the energy deposited by ion beams in carbon nanotubes. [ABSTRACT FROM AUTHOR]

Small lanthanum oxide clusters were produced in a laser-ablation molecular beam setup and studied by mass spectrometry and laser threshold photoionization spectroscopy. Mass spectrometry investigations of neutral clusters revealed certain stoichiometries, (La2O3)n and (La2O3)n.LaO (n = 1–6) were stable. For cation clusters, similar stoichiometric preference was reported by previous authors. The stoichiometric preference of the oxides was not affected by oxygen concentrations. Ionization thresholds and vertical ionization energies (VIEs) were measured for the (La2O3)n.LaO (n = 1–3) neutral clusters from the photoionization efficiency curves. The energetically low-lying structural isomers for these clusters along with their adiabatic and vertical ionization energies were computed from the density functional theory using B3LYP and PW91GGA exchange correlation functionals. Favorable agreement between the computed and experimental ionization energies allows assignments of the ground state structures for these clusters. For La3O4, a C3v-like structure has been found as the ground state built on La-O-La bonds with their usual oxidation states of +3 for La and −2 for O atoms. For larger clusters La5O7 and La7 O10, however, a trend towards forming more compact structures with few metal and O sites having higher coordination numbers have been found as the ground states and are suggested to be present in the molecular beam. [ABSTRACT FROM AUTHOR]