A formalism is derived to include the effects of the longhyphen;range attractive part of the interaction potential in the calculation of atomndash;diatom collision cross sections using the impulse approach (IA). These calculations have, until now, assumed the atomndash;diatom potential given by a sum of two atomndash;atom interactions, consequently yielding a poor representation of the longhyphen;range attractive part. In the distorted wave impulse approach (DWIA) the longhyphen;range attractive part, located at the center of mass of the diatom, is a spherically symmetric potential which lsquo;lsquo;distortsrsquo;rsquo; the incoming and outgoing waves. The DWIA formalism is used to calculate differential cross sections for the rotationally inelastic process Li++N2(v=0,thinsp;j=2)rarr;Li++N2(vrsquo;=0,thinsp;jrsquo;), as a function of the final rotational leveljrsquo;, at a relative kinetic energy of 4.23 eV and center of mass scattering angles of 49.2deg; and 37.1deg;. 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 atomndash;atom interactions expressed by either hardhyphen;core, or exponential repulsive, functions.
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