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

In the space-fixed frame, a novel angular decoupling approximation has been developed 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, the ''decoupled l-dominant'' (DLD) method is expected to be best suited for the study of collisions in which strong long-range forces play a major role. The DLD method was applied 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