Articles you may be interested inFrozen rotor approximation in the mixed quantum/classical theory for collisional energy transfer: Application to ozone stabilization Towards quantum mechanical description of the unconventional mass-dependent isotope effect in ozone: Resonance recombination in the strong collision approximationWe present a quantum-mechanical model for termolecular association reactions XYϩZϩM→XYZϩM involving the formation of a long-lived complex XYZ*. The rotation of the molecule XYZ is treated in the infinite order sudden approximation ͑IOS͒ and its vibrations are treated by the coupled-channel method ͑VCC͒. Resonances featuring the XYZ* long-lived complex formation are first computed by means of the stabilization method and are then included in the vibrational basis functions used for the inelastic VCC-IOS scattering calculation. The method yields rate constants for the association process selected in resonance and bound states of XYZ. We apply the method to the formation of ozone and investigate isotope effects. Calculations of energy transfer and collision-induced recombination of OϩO 2 in collision with Ar are reported for a range of ozone isotopomers. The bending mode of O 3 is not treated explicitly in these computations. The results establish a strong selectivity in vibrational state-to-state cross sections for the deactivation of O 3 during the collisional energy transfer process with Ar. The present calculations also account for the high sensitivity of rate constants with respect to the isotopic composition of ozone molecules but not in the same proportion as experiments. The energy transfer from selected initial vibrational states is also calculated as a function of the initial relative kinetic energy.

A quantum-mechanical model is designed for the calculation of termolecular association reaction rate coefficients in the low-pressure fall-off regime. The dynamics is set up within the energy transfer mechanism and the kinetic scheme is the steady-state approximation. We applied this model to the formation of ozone O + O2 + M --> O3 + M for M = Ar, making use of semiquantitative potential energy surfaces. The stabilization process is treated by means of the vibrational close-coupling infinite order sudden scattering theory. Major approximations include the neglect of the O3 vibrational bending mode and rovibrational couplings. We calculated individual isotope-specific rate constants and rate constant ratios over the temperature range 10-1000 K and the pressure fall-off region 10(-7)-10(2) bar. The present results show a qualitative and semiquantitative agreement with available experiments, particularly in the temperature region of atmospheric interest.

The R-matrix Floquet theory is applied to the study of electron-hydrogen scattering in the presence of a CO 2 laser field. One-electron models are first considered in which the target is represented by a potential. Results are also presented for an explicit two-electron calculation, including 1s, 2s and 2p orbitals of hydrogen. Angular distributions are in fairly good agreement with those of the low-frequency approximation, even when the momentum transfer is almost perpendicular to the polarization of the field.The study of electron-atom scattering in intense laser fields has received an important stimulus since Wallbank and Holmes (1993, 1994a, b) measured angular distributions much larger than those predicted by the low-frequency formula (LFF) (Kroll and Watson 1973, Krüger and Jung 1978, Rosenberg 1981. The experiments were performed using a CO 2 laser for geometries in which the momentum transfer is almost perpendicular to the polarization of the field. In these conditions, the expansion parameter of the original Kroll and Watson low-frequency formula diverges. There have subsequently been a number of attempts to improve the theoretical description of laser-assisted electron-atom scattering. Madsen and Taulbjerg (1995) have derived a generalization of the Kroll and Watson formula in the weakfield regime which is valid for all geometries, but there is still substantial disagreement with experiment. Chen and Robicheaux (1996) applied an approximate R-matrix Floquet method and a diabatic approximation to study laser-assisted scattering using a model potential representing an argon target. Both calculations yielded results in good agreement with the predictions of the LFF. Milosević and Ehlotzky (1997) investigated electron scattering by Yukawa potentials in the presence of a laser field. Their work is based on an off-shell low-frequency approximation combined with a Padé acceleration technique. They concluded that off-shell effects cannot explain the discrepancy between the measurements and the LFF results.On the other hand, several authors have obtained angular distributions in the forward direction much larger than those predicted by the LFF. Geltman (1996, 1997) solved a model one-electron problem perturbatively with an outgoing wave in the final state, instead of the usual ingoing wave. Cionga et al (1997) applied a Floquet close-coupling method to calculate angular distributions of electron-hydrogen scattering with absorption and emission of up to three photons, at a laser intensity much lower than that used in the experiments. Recently, Jaroń and Kamiński (1997) suggested that the breakdown of the LFF could be attributed to the neglect of off-shell effects. They found these to be important for small-angle

The R-matrix Floquet method is used to study electron-helium scattering in a Nd-YAG laser in the energy range from 0.65 to 0.78 Hartree. The effect of strong AC Stark mixing between the 1s2s 3 S and 1s2p 3 P o states is discussed. Integrated cross sections for elastic scattering and excitation from the ground state into the triplet states are presented. The He − (1s2s 2 2 S) resonance is shown to be a dominant feature below the field-free threshold.