J. Sogas

Electronic excitation and charge transfer processes in collisions between Mg(3 1S0) atoms and Rb+(1S0) ions in the 0.07–4.00 keV energy range

Inelastic collision processes between neutral Mg atoms and Rb(+) ions, both in their ground states, have been studied by means of a crossed molecular beam technique measuring the decay fluorescence of the excited species formed. Emissions corresponding to Mg(3 (1)P(1)), Mg(3 (3)D(3,2,1)), and Mg(4 (3)S(1)), formed by direct target excitation, Rb(5 (2)P(3/2,1/2)), Rb(6 (2)P(3/2,1/2)) produced by electron capture and also the phosphorescent emission due to decay of Mg(3 (3)P(1)), have been detected and the corresponding absolute cross-section values measured both as total values and resolved into their J states. No polarization measurements could be made. Ab initio calculations using pseudopotentials have been performed and from these a manifold of adiabatic energy curves correlating with the different entry and exit channels have been obtained, allowing to propose a qualitative interpretation of the results, such as the shape of the cross section vs energy for different transitions and the oscillating nature of the branching ratios due to interference effects.

An experimental guided-ion-beam and ab initio study of the ion-molecule gas-phase reactions between Li+ ions and iso-C3H7Cl in their ground electronic state.

Reactive collisions between Li(+) ions and i-C(3)H(7)Cl molecules have been studied in the 0.20-12.00 eV center-of-mass energy range using an octopole radio frequency guided-ion beam apparatus recently developed in our laboratory. At low collision energies, dehydrohalogenation reactions giving rise to Li(C(3)H(6))(+) and Li(HCl)(+) are the main reaction channels, while at higher ones C(3)H(7)(+) and C(2)H(3)(+) become dominant, all their reactive cross sections having been measured as a function of the collision energy. To obtain information about the potential energy surfaces (PESs) on which the reactive processes take place, ab initio calculations at the MP2 level have been performed. For dehydrohalogenations, the reactive ground singlet PES shows ion-molecule adduct formation in both the reactant and product sides of the surface. Following the minimum energy path connecting both minima, an unstable intermediate and the corresponding barriers, both lying below the reactants energy, have been characterized. The entrance channel ion-molecule adduct is also involved in the formation of C(3)H(7)(+), which then generates C(2)H(3)(+) via an CH(4) unimolecular elimination. A qualitative interpretation of the experimental results based on ab initio calculations is also included.

Inelastic electronic excitation and electron transfer processes in collisions between Mg(3S01) atoms and K+(S01) ions studied by crossed beams in the 0.10-3.80-keV energy range

Inelastic and charge-transfer excitation processes in collisions between ground-state neutral Mg atoms and K+ ions have been studied by means of a crossed molecular-beam technique. Decay fluorescent emissions from Mg(3 1P1),Mg(4 3S1), and Mg(3s(1)3d(1), 3(3)D3,2,1) as well as the phosphorescent emission due to Mg(3 3P1) have been observed from excited Mg atoms and the charge-transfer emission decays from K(4 2P 3/2,1/2), K(5 2P 3/2, 1/2), K(6 2S 1/2), and K(4 2D 5/2, 3/2) for excited K atoms. The corresponding absolute cross-sections values versus collision energy functions were determined in the 0.10-3.80 keV laboratory energy range. In order to interpret the experimental results, accurate ab initio full configuration-interaction calculations using pseudopotentials have been performed for the (Mg-K)+ system, giving a manifold of adiabatic singlet and triplet potential-energy curves correlating with the different collision channels, which allow a qualitative interpretation of the emission excitation functions measured for the different processes studied. A comparative study with other Mg-alkali ion systems previously studied is also included.

Crossed ion–atom beam study of the inelastic collision processes between neutral Mg(3 1S0) atoms and Cs+(1S0) ions in the 0.05–4.20 keV energy range

Inelastic excitation and charge transfer excitation processes in collisions between neutral Mg atoms and Cs+ ions, both in their ground states, have been studied by means of a crossed molecular beam technique. Decay fluorescent emissions from Mg(3 1P1), Mg(3 3D3,2,1), Mg(4 3S1) and Cs(6 2P3/2) states have been detected as well as the phosphorescent emission due to Mg(3 3P1) decay. The corresponding absolute cross-sections vs. collision energy functions were determined in the laboratory 0.05–4.20 keV energy range. In order to interpret the experimental results, accurate ab initio calculations using pseudopotentials have been performed for the (Mg–Cs)+ system obtaining a manifold of adiabatic energy curves correlating with the different collision channels and allowing a qualitative interpretation of the emission excitation functions for the different processes studied.

Study of electronic excitation and electron capture processes in the collision between ground-state rubidium atoms and potassium ions by crossed beams

Collisional processes between K ions and Rb (both in their ground state) have been studied using a crossed beam technique and measuring the decay fluorescence. Emissions corresponding to decay of the first excited state of Rb and the first two excited states of neutral K have been detected. For these, absolute total cross-section dependence on collision energy, branching ratios between J-states and true excitation cross-sections (from polarization measurements) have been determined, all in the 0.3–4.1 keV range. The results are interpreted using adiabatic potential energy curves calculated ab initio employing one-electron, non-empirical, relativistic pseudopotentials and including core polarisation.

Rb(52P1/2,3/2) and Rb(62P1/2,3/2) formation in Rb(52S1/2)+Rb+(1S0) collisions by crossed molecular beams

Abstract Total cross-sections for collisions between Rb + and Rb, leading to the formation of the excited states related to the electronic configurations Rb(5p) and Rb(6p), have been determined as the sum of those corresponding to direct electronic excitation and to electron capture processes in the 0.3–4.2 keV energy range in the laboratory frame. For Rb(5p) the branching ratio between its J-states has been also determined as well as that of the m J for the Rb(5 2 S 1/2 )→Rb(5 2 P 3/2 ) excitation.

Electronic excitation and electron capture processes in the collision between Rb atoms and Na ions by crossed molecular beams

Abstract Cross section dependence on collision energy (0.1–5.0 keV) has been determined for exit channels Rb(5 2 P 1/2,3/2 ) and Na(3 2 P 1/2,3/2 , 4 2 D 5/2,3/2 , 5 2 D 5/2,3/2 , 7 2 S 1/2 , 6 2 D 5/2,3/2 ) in the Rb+Na + collision. Branching ratios between different J -components are also reported for the first two channels. Polarisation measurements have made it possible to obtain magnetic cross sections for the Na(3 2 P 3/2 ) formation. Results for the first electron capture have been interpreted qualitatively in terms of a linear Landau–Zener–Stuckelberg model and ab initio calculations.

Crossed Beams and Theoretical Study of the (NaRb)+ Collisional System

Ion-atom collisions are one of the most assiduously studied topics in Chemical Dynamics, since their relative simplicity make their study easy to set up and carry out. When both colliding species are alkali atoms this interest becomes still greater, not only because their dynamics can be studied using simple models such as those involving pseudopotentials, but also because species in excited electronic states are readily formed by the collisions (either by direct excitation or via electron exchange processes) whose fluorescent decay emissions can furnish useful information and offer the perspective of such interesting technical applications as lasers and gas-discharge lamps. While beam-chamber experiments were very easy to perform on these systems, it was the development of the crossed beams technique that finally permitted their study in carefully selected conditions to obtain true cross-section data. Foremost in this field were Aquilanti el al whose work included the determination of collision cross-sections for a number of symmetrical and unsymmetrical collision systems, being able in some cases to resolve the fluorescent emissions into their J-components, and even to study polarisation fractions accurately enough to determine the branching ratios between MJ states (for a full review of papers in this field see [1] and references mentioned there).

Role of the BO bond in the reaction dynamics of BO+H2→HBO+H

An extensive quasiclassical trajectory study of the dynamics of the title reaction has been carried out on a six-dimensional, analytical potential energy surface, with the goal of understanding the role of the BO bond. For this purpose, trajectories for different hypothetical isotopes of the BO molecule have been calculated, for selected rovibrational levels of the reactants, at low and moderate collision energies. For all these cases, a clear departure from the BO bond spectator behaviour, as well as an unexpected role of hindered rotation normal modes at the transition state, is found.

An experimental study of electronic excitation and electron capture processes in Rb(52S1/2) collision with Cs+ and Li+ ions

The collisional systems Rb–Cs+ and Rb–Li+ (with all species in the ground entrance channel) have been studied using the crossed beams technique combined with decay fluorescence measurements. In the former system, only the emissions from the excited atoms Rb(52P1/2,3/2) and Cs(72P1/2,3/2) have been observed, while for the latter the electron exchange channels Li(22P1/2,3/2) and Li(32P1/2,3/2) were present, all of them giving signal strengths much lower than those shown by the same processes for other alkali atom–alkali ion collisional pairs.The collision energy–excitation cross section dependence for all four channels has been determined, as well as the branching ratio between J-states for those involving Cs ions as projectiles. A qualitative interpretation of the observed inelastic processes is performed using abinitio one-electron calculations.