A DISTORTED-WAVE IMPULSE APPROACH FOR ATOM DIATOM COLLISIONS

A formalism is derived to include the effects of the long-range attractive part of the interaction potential in the calculation of atom-diatom collision cross sections using the impulse approach (IA). These calculations have, until now, assumed the atom-diatom potential given by a sum of two atom-atom interactions, consequently yielding a poor representation of the long-range attractive part. In the distorted wave impulse approach (DWIA) the long-range attractive part, located at the center of mass of the diatom, is a spherically symmetric potential which ''distorts'' the incoming and outgoing waves. The DWIA formalism is used to calculate differential cross sections for the rotationally inelastic process Li+ + N2(v=0, j=2) Li+ + N2(v'=0, j'), as a function of the final rotational level j', at a relative kinetic energy of 4.23 eV and center of mass scattering angles of 49.2-degrees and 37.1-degrees. It is shown that differential cross sections calculated using the DWIA formalism are in much better agreement with experimentally measured ones than IA differential cross sections using atom-atom interactions expressed by either hard-core, or exponential repulsive, functions.