A decoupled l-dominant approximation for ion–molecule and atom–molecule collisions

Abstract

In the space-fixed frame we develop a novel angular decoupling approximation, which involves the degree of alignment between the molecular and total rotational angular momentum vectors. When grafted onto the recent l-dominant method, this decoupling results in a set of block-diagonalized coupled equations of dimensionality equivalent to that of the body-fixed coupled-states (CS) equations. In direct contrast to the CS method, we expect the ’’decoupled l-dominant’’ (DLD) method to be best suited for the study of collisions in which strong long-range forces play a major role. We have applied the DLD method to the determination of partial and total cross sections for rotationally inelastic Ar–N2 and Li+–H2 collisions. The agreement with exact close-coupling values is very satisfactory, except in those cases where collisions at large impact parameter do not contribute significantly to a particular transition.