Rovibrational product state distribution for inelastic H+D2 collisions

Experimental measurements of rovibrational product state distributions for the inelastic scattering process H + D2(nu=0,j)-->H + D2(nu' = 1,2,j') are presented and compared with the results of quasiclassical and quantum mechanical calculations. Agreement between theory and experiment is almost quantitative. Two subtle trends are found: the relative amount of energy in product rotational excitation decreases slightly with increasing collision energy and increases slightly with increasing product vibrational excitation. These trends are the reverse of what has been found for reactive scattering in which the opposite trends are much more pronounced.     

Classical dependence of polarization on potential energy surface in rotationally inelastic collisions

Quasiclassicol trajectory calculations have been performed for model potential energy surfaces to investigate polarization in (j,m_j) → (j',m_j) integral cross sections For j = 0, it was found that the occurrence of polarization requires an attractive well, and that it be in the collinear configuration Results for j≠ 0 are also presented.     

Selection rules for collisional energy transfer in homonuclear diatomics. rotationally inelastic collisions

We have made a precise study of the circular polarisation of rotationally resolved features of laser-excited iodine. The J′ = 19, ν′ = 16 level of ³II⁺_ou was excited using circularly polarised dye-laser fluorescence and a quantitative data on polarisation features representing inelastic transfer of ΔJ′ = 30 was recorded. The experimental circular polarisation ratios were compared to those predicted by two totally conserving models, ΔM = 0 and Δθ = 0. The agreement between experimental points and the predictions based on the former lead to the formation of a new selection due on rotationally inelastic transfer namely, ΔM = 0.     

Stationary phase analysis of inelastic atomic collisions: Penning ionization

Analytica semi-classical expressions, based on a stationary phase analysis, are presented for the energy distribution of particles ejected in inelastic processes. The tabulation of basic functions yields a considerable savings of computer time. Numerical comparisons with quantal calculations are made for the Penning ionization process involving metastable helium and atomic hydrogen, using two different potentials proposed for the He*H(²Σ) state.     

An ab initio treatment of inelastic H + Ne collisions at low energy

On the basis of published quantum chemical data, we calculate the integral cross section for the inelastic process H(1s) + Ne → H(2s, 2p) + Ne for collision energies between threshold and 1.5 keV. Though the quantum chemical data are not completely unambiguous and not so complete as desired, a reasonable agreement between experiment and theory can be achieved.     

Partial differential cross sections for inelastic He++Ne collisions at low energy

We report differential cross section measurements with high angular resolution for different channels of the inelastic processes He⁺+Ne→He⁺+Ne* and He⁺+Ne→He*+Ne⁺, for collision energies between 100 and 200 eV. For the Ne states (2p ⁵3s)^1,3 P ₁, which decay optically, we determined the fraction with the alignment at right angles to the scattering plane. The results are used to discuss the mechanism of the processes and the influence of the spin-orbit interaction upon the collision.     

Elastic and inelastic angular distributions in the jz-conserving coupled states approximation for molecular collisions

An approximation scheme is described which allows the decoupling of molecular rotational j and l angular momenta in molecular collisions. With a particular choice of the interaction potential, the potential matrix couples only the molecular states of the system and in particular those in which the z-axis projection of j is conserved. Test calculations on He + H₂ for the elastic j = O → O and rotationally inelastic j = O → 2 differential cross sections are presented in the energy range 0.1 to 0.9 eV. These results are compared with the full coupled-channel cross sections and are found to be extremely accurate.     

Effects of electron kinetic energy and ion-electron inelastic collisions in electron capture dissociation measured using ion nanocalorimetry

Ion nanocalorimetry is used to measure the effects of electron kinetic energy in electron capture dissociation (ECD). With ion nanocalorimetry, the internal energy deposited into a hydrated cluster upon activation can be determined from the number of water molecules that evaporate. Varying the heated cathode potential from -1.3 to -2.0 V during ECD has no effect on the average number of water molecules lost from the reduced clusters of either [Ca(H2O)15]2+ or [Ca(H2O)32]2+, even when these data are extrapolated to a cathode potential of zero volts. These results indicate that the initial electron kinetic energy does not go into internal energy in these ions upon ECD. No effects of ion heating from inelastic ion-electron collisions are observed for electron irradiation times up to 200 ms, although some heating occurs for [Ca(H2O)17]2+ at longer irradiation times. In contrast, this effect is negligible for [Ca(H2O)32]2+, a cluster size typically used in nanocalorimetry experiments, indicating that energy transfer from inelastic ion-electron collisions is negligible compared with effects of radiative absorption and emission for these larger clusters. These results have significance toward establishing the accuracy with which electrochemical redox potentials, measured on an absolute basis in the gas phase using ion nanocalorimetry, can be related to relative potentials measured in solution.     

Theoretical study of inelastic collisions of hot atoms

In this work, use is made of the integral-equation approach to study inelastic collisions so frequently encountered in hot-atom chemistry. To do this a few assumptions are made which on the one hand enable the analytic derivation and on the other hand are still real enough in the sense that the solution obtained is valid and meaningful. It is found that the inelasticity in the collision between a hot atom and a reactive molecule manifests itself as a parameter which can be defined only by analogy as the average energy loss in an inelastic collision.     

Energy transfer in reactive and nonreactive collisions of Na with Na2

Stimulated by the experimental finding of vibrationally and rotationally cold dimers in supersonic nozzle molecular beams of sodium, we have studied energy transfer in collisions of Na with Na₂ over a wide range of initial relative translation energies E and impact parameters b by a classical mechanical trajectory method. The vibrational and rotational energies were initialized using Boltzmann distributions characterized by temperatures T_vib = 150 K, T_rot = 50 K. We find that for large values of E the energy transfer in reactive collisions increases with b while it decreases with b for the nonreactive collisions. For low values of E, energy transfer is a decreasing function of b for both reactive and nonreactive encounters. Both the reactive and nonreactive mechanisms are very efficient in effecting transfer, between 40–70% of the initial relative translational energy is converted into internal energy of the diatom, leading to the conclusion that the reverse collisions would result in the rapid relaxation observed in experiment.     

Joint products'' state distributions in molecular collisions

A functional form for the surprisal containing a correlation term is shown to account well for the joint (e.g. vibrational) products' state distributio     

Ionizing collisions of potassium atoms with molecules: Excitation energy of the product molecular ion

For processes of the type K + M

K⁺ + M^? at eV collision energies, measurements are reported of the population of excited states of the product negative ions. For M = Br₂ and SF₆ only a small excitation (0.5 – 3 eV) is found. For M = O₂, the products can be excited up to higher energies (? 5 eV); this is ascribed to a second electronic channel of the process.     

Vibrational energy transfer in non-reactive molecular collisions: An information-theoretic analysis

Experimental and (trajectory) computed rates of vibrational relaxation of molecules in selected internal states are analyzed. A dynamic constraint is identified. The entire array of (vibrational) manifold-to-manifold rate constants (at a given temperature) is shown to be characterized by this constraint and hence yield a linear surprisal plot. It is argued that bulk measurements of the vibrational relaxation time in a buffer gas will suffice to determine the single parameter in the dynamic constraint.     

Low-energy rotational inelastic collisions of H(+) + CO system

The quantum mechanical state-to-state rotational excitation cross sections have been computed using the ab initio ground electronic state potential energy surface of the system [M. Mladenovic and S. Schmatz, J. Chem. Phys. 109, 4456 (1998)] computed at coupled-cluster single and double and triple perturbative excitations method using correlation-consistent polarized valence quadruple zeta basis set where the asymptotic potential have been computed using the dipole moment, quadrupole moment, and the molecular polarizability components and fitted to this interaction potential. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The integral cross sections for rotational excitations have been computed by solving close-coupled equations at very low collision energies (5-200 cm(-1)) and the corresponding rates have been obtained for a range of low temperatures (5-175 K). The j = 0 → j(') = 1 rotational excitation cross section (and rate) is found to be the dominant followed by the j = 0 → j(') = 2 in these collision energies. The close-coupling, coupled-state, and infinite-order sudden approximations coupling calculations have been performed in the energy range of 0.1-1.0 eV using vibrational ground potential. The rotational cross sections have been obtained by performing computationally accurate close-coupling calculations at 0.1 eV using vibrationally averaged potential (ν = 1) and compared with the results of vibrational ground potential.     

Millimeter-wave time-resolved studies of HCO+-H2 inelastic collisions

A novel ion cell has been constructed for the purpose of studying rotationally inelastic collisions involving truly thermal molecular ions at low temperatures. With this ion cell, time-resolved double resonance (pump-probe) spectroscopic experiments have been performed to determine the cross sections for relaxation of the J = 2 state of HCO+ in collisions with normal-H2 at temperatures around 40 and 77 K. The HCO+ is pumped through the J = 2<--1 transition and probed via the J = 3<--2 transition. The cross sections at the lower temperature are slightly below those predicted by the simple Langevin theory, while those at the higher temperature are in good agreement with this theory.     

R-matrix theory of inelastic processes in low-energy electron collisions with HCl molecule

The processes of vibrational excitation and dissociative attachment in low-energy electron collisions with HCl molecule are considered. TheR matrix theory of these processes incorporating nuclear dynamics is developed. The input data of the theory are characteristics of the systeme-HCl calculated in the fixed-nuclei approximation. The comparison with experimental data and other theories is given. It is shown that the account of the nuclear motion leads to the significant increase of the vibrational excitation cross sections near threshold. However, in the present variant of the theory, the cross sections for the excitation of the first level are essentially lower than the experimental ones. The dissociative attachment cross sections are in good agreement with the experiment.     

Propensity rules in rotationally inelastic collisions of CO2

Propensity rules for the rotational quantum number dependence of cross sections for CO₂ collisions with atoms are predicted to have subtle characteristics for transitions involving levels in excited vibrational angular momentum states.     

Rotational-translattonal energy exchange in molecule-surface collisions

Reported are calculations of rotational energy transfer in collisions of Cl₂ molecules with a rigid, smooth surface, using both sudden approximations and quasi-classical trajectories. High probabilities are found for very large Δj transitions compared to corresponding gas-phase collisions: thus molecular collisions with walls can be extremely efficient in producing rotational transitions.