REORIENTATION DIFFERENTIAL CROSS-SECTIONS AT HIGH-ENERGY

The angular momentum decoupling approximations, used extensively in approximate calculations for complex systems, are evaluated here in extensive comparisons with exact calculations for a heteronuclear system with a moderately large dipole moment at high enough energy that there are many open rotational states. Orientation-dependent differential cross sections for He-SiO rigid-rotor scattering calculations at high translational energy are presented. Coupled states and recoupled states results are compared with those of close coupling at a total energy of 27 meV. Although the coupled states (CS) method approximates exact calculations by ignoring m coupling in the body frame, the l-averaged CS results are good for orientation-dependent differential cross sections. The l-averaged form of recoupled states makes significant improvements over the l-averaged form of coupled states for orientationally elastic transitions and for large-j transitions. As in past studies, the l-initial and l-final forms of coupled and recoupled states are found to be inferior to the l-averaged form. Orientation-dependent integral and degeneracy-averaged differential and integral cross sections are also discussed.