Adiabatic distorted wave infinite order sudden (ADWIOS) approximation for the calculation of inelastic molecular collision cross sections

Journal Article · Wed Aug 01 04:00:00 EDT 1979 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.438449· OSTI ID:6095944

Eno, L; Balint-Kurti, G G

A new approximate method is presented for the rapid calculation of vibrationally--rotationally inelastic molecular collision cross sections. The method treats the coupling between the rotational states, belonging to the same vibrational level, using the sudden approximation. The vibrational states are treated using an adiabatic basis. With this basis it is found that a first order distorted wave approximation gives good agreement with fully converged close coupling calculations. Some previously developed techniques are extended to permit reliable analytic expressions to be formulated for the angle fixed S matrix elements which appear in the theory. The great computational efficiency of the method is based on these analytic formulas which eliminate the need for the numerical solution of differential equations and for the numerical evaluation of difficult integrals. The angle fixed S matrices which result are then treated within the framework of the recently developed sudden approximation to yield inelastic cross sections. The method is applied to the calculation of vibrationally--rotationally inelastic cross sections for the He+H/sub 2/ system and comparisons are made with close coupling calculations which are fully converged in both rotational and vibrational basis. Analysis of the results shows that for the He+H/sub 2/ system the sudden approximation fails significantly within the n=1 vibrational manifold at total energies below 1.1425 eV but the validity of the approximation clearly improves with increasing energy. The He+He/sub 2/ system was used in the present work as it was the only suitable one for which exact calculations were available in the literature for comparison purposes. For heavier systems the sudden approximation will be valid at much lower energies.

• Research Organization: School of Chemistry, Bristol University, Bristol BS8 ITS, United Kingdom
• OSTI ID: 6095944
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 71:3; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
COLLISIONS
CROSS SECTIONS
CRYOGENIC FLUIDS
DISTORTED WAVE THEORY
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FLUIDS
HELIUM
HYDROGEN
INELASTIC SCATTERING
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
NONMETALS
RARE GASES
ROTATIONAL STATES
SCATTERING
SUDDEN APPROXIMATION
VIBRATIONAL STATES