Accuracy of the IOS approximation for highly inelastic RET collisions

Inelastic collisions which give rise to rotational energy transfer (RET) at several different relative energies are examined for He and Ar projectiles interacting with N2. Calculations are carried out within the infinite order sudden approximation (IOSA) for the dynamics and repeated more accurately by keeping the centrifugal sudden approximation (CSA) only in the quantum treatment of the multichannel scattering. It is shown that IOS invariably overestimates the CS cross sections, especially when high Δj transitions are involved. An average index to measure the overall efficiency of the RET processes is defined and compared within the two dynamical approximations. From such an index one can extract scaling corrections for the corresponding IOSA quantity and some measure of the global anisotropy for the chosen atom-diatomic potential surfaces