The argon hydrogen–fluoride differential scattering cross section

Abstract

The total differential cross section for Ar–HF was measured at a collision energy of 1637 K (141 meV). Although diffraction oscillations were not resolved, a broad primary rainbow peak was observed. Scattering calculations were carried out for the Ar–HF interaction potentials developed by Douketis et al. and Hutson and Howard. The spherical potential and infinite order sudden approximations do not give a good description of the total differential scattering. The final-l labeled coupled states approximation, on the other hand, is in good agreement with the more accurate close coupled approximation. Neither potential predicts cross sections which are in good agreement with the measured scattering intensities. Contributions to the total scattering from elastic and inelastic processes were investigated using the coupled states approximation. The contributions to the total scattering from different initial HF rotational states were also studied. The total scattering for j initial=0 differs significantly from that for other values of j initial. It is therefore important to know the distribution of rotational states in the HF beam if one is to compare calculated total differential cross sections with measured ones. The largest inelastic cross section is for the j=0 to j′=1 transition. Collisions in which the Ar atom interacts strongly with the anisotropic potential well, rather than near head-on collisions off the repulsive wall of the potential, are responsible for the large j=0 to j′=1 cross section. The results of accurate SCF calculations for Ar–HF are also reported in this paper.