skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Comment on 'Entropy lowering in ion-atom collisions'

Abstract

The recent experimental result by Nguyen et al. [Phys. Rev. A 71, 062714 (2005)] on the ratio of cross sections for charge exchange processes Rb{sup +}+Rb(5s){yields}Rb(5p)+Rb{sup +} and Rb{sup +}+Rb(5p){yields}Rb(5s)+Rb{sup +} is quantitatively derived from simple considerations within the general framework of the quasimolecular theory. Contrary to the expectations, applicability of the Demkov model for charge exchange with small energy defect is not shattered.

Authors:
 [1]
  1. V. Fock Institute of Physics, St Petersburg State University, St Petersburg 198504 (Russian Federation) and Max Planck Institute for the Physics of Complex Systems, Noetnitzer Strasse 38, D-01187, Dresden (Germany)
Publication Date:
OSTI Identifier:
20786812
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 73; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevA.73.016702; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CHARGE EXCHANGE; CROSS SECTIONS; ENTROPY; ION-ATOM COLLISIONS; P STATES; RUBIDIUM; RUBIDIUM IONS; S STATES

Citation Formats

Ostrovsky, V. N.. Comment on 'Entropy lowering in ion-atom collisions'. United States: N. p., 2006. Web. doi:10.1103/PHYSREVA.73.0.
Ostrovsky, V. N.. Comment on 'Entropy lowering in ion-atom collisions'. United States. doi:10.1103/PHYSREVA.73.0.
Ostrovsky, V. N.. Sun . "Comment on 'Entropy lowering in ion-atom collisions'". United States. doi:10.1103/PHYSREVA.73.0.
@article{osti_20786812,
title = {Comment on 'Entropy lowering in ion-atom collisions'},
author = {Ostrovsky, V. N.},
abstractNote = {The recent experimental result by Nguyen et al. [Phys. Rev. A 71, 062714 (2005)] on the ratio of cross sections for charge exchange processes Rb{sup +}+Rb(5s){yields}Rb(5p)+Rb{sup +} and Rb{sup +}+Rb(5p){yields}Rb(5s)+Rb{sup +} is quantitatively derived from simple considerations within the general framework of the quasimolecular theory. Contrary to the expectations, applicability of the Demkov model for charge exchange with small energy defect is not shattered.},
doi = {10.1103/PHYSREVA.73.0},
journal = {Physical Review. A},
number = 1,
volume = 73,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • In ion-atom collisions, the charge transfer cross section is typically a strong function of the energy defect or Q value, typically with smaller energy defects giving rise to higher capture probabilities. In some theoretical treatments, for example those based on the Demkov model, the cross section is a strong function of the magnitude of the Q value, but is independent of its sign. In order to test this predicted sign independence, one must compare capture cross sections from energetically symmetric collision channels. In this work, relative capture cross sections, differential in scattering angle, are measured and compared for the energeticallymore » symmetric channels: Rb{sup +}+Rb(5s){yields}Rb(5p)+Rb{sup +} and Rb{sup +}+Rb(5p){yields}Rb(5s)+Rb{sup +}. It is found that not only are the two cross sections not equal, but that in this case the endoergic channel was 3 times more likely. That is, the entropy reducing channel was preferred. An intuitive model, based on molecular potential curves, is suggested. The endoergic propensity is found to be consistent with this model.« less
  • A Comment on the Letter by Hansen {ital et} {ital al}., Phys. Rev. Lett. 64, 2491 (1990).
  • It is shown that the procedure described by Olson and Salop for classical-trajectory Monte Carlo treatment of ion-atom collisions does not provide a uniform statistical distribution of all the parameters defining the initial conditions of a trajectory. Impact-ionization and charge-transfer cross sections for collisions of H/sup +/ with H at H energies between 25 and 600 keV are recalculated eliminating this failing and compared with those obtained using the procedure of Olson and Salop and with experimental results.
  • Consideration is given to certain aspects of inelastic collisions. The semi-empirical use of complex phase shifts to allow for the occurrence of such differences is first discussed and related to the concept of complex scattering potentials. Scattering by an absorbing sphere is then considered and shown to involve elastic shadow scattering. This is related to certain experimental results on the angular distribution of He/sup +/ ions scattered by Kr and Xe atoms. Complex phase shift analysis is then extended to collisions between H and H/sup -/ in which both charge transfer and detachment may occur. A description is given ofmore » the experimental method used to measure these cross sections and of the relation of the observed results to the theory. Finally, a discussion of curve-crossing perturbations in elastic scattering and their relation to inelastic scattering is given. It is shown that these effects account for certain observed phenomena in the elastic scattering of ions by atoms which were not explicable in terms of the analysis given previously. (auth)« less