Differential Cross Sections for (R,T) energy transfer in He-HF collisions: comparing theory with experiments.

Starting from a recently proposed potential energy surface, the relative occurrence of rotational inelasticity during He-HF collisions at thermal energies is examined as a function of scattering angle by employing both rigorous ab initio calculations (CC) and approximate solutions of the scattering equations (IOSA). The chosen range of energy is the same as one recently studied in highly accurate molecular beam experiments, so that rather close scrutiny of the computational outcome is made possible by comparison with measured differential cross sections (DCS) over a wide angular region well beyond the rainbow angle. The possible effect of isotopic substitution and the reliability of energy sudden schemes are investigated by computing both total and individual DCS involving rotational transitions. A very satisfactory fit to the measured total DCS is found within the IOSA approximation, thus providing further checks on the quality level of the employed potential surface. The general inefficiency in this system of energy deposition into rotations at thermal collision energies is here indicated by both theory and experiments.