Sudden Approximation Applied to Rotational Excitation of Molecules by Atoms. II. Scattering of Polar Diatomics

The sudden approximation is applied to the computation of rotational transition probabilities and inelastic total cross sections for the scattering of polar and nonpolar diatomic molecules (rigid rotors) by atoms. The calculations are based upon an interaction potential which includes both short- and long-range anisotropies. At thermal energies the long-range attractive parts of the potential are of principal importance in determining the inelasticity, with a significant contribution arising from the quadrupole interaction term (varying as R−7 cos3Θ). The computations show the rapid onset of ``dominant-coupling'' behavior (randomization of transition probability among all close-coupled states) for impact parameters below about (S/π)½, where S is the total inelastic cross section.