EVIDENCE FOR THE DEEP POTENTIAL WELL OF LI+HF FROM BACKWARD GLORY SCATTERING

Angular distributions of Li scattered from HF have been measured for various collision energies E(tr) ranging from 64 to 372 meV. At E(tr)=88 and 64 meV a clear rainbow structure at small angles is observed. At E(tr)=296 meV a faint peak emerges at large angles which becomes a prominent feature for all lower energies. The position of the peak always corresponds to backward scattering in the center-of-mass frame. This fact and the rather sudden rise of the backward intensity with decreasing E(tr) clearly identify this phenomenon as a backward glory. Based on the infinite order sudden approximation both the rainbow and the backward glory as well as the E(tr) dependence of these features could be rationalized using a simple empirical potential energy surface. The surface consists of two only moderately anisotropic extended regions which differ drastically in the well depths. The shallow well region has a maximal depth of almost-equal-to 33 meV and is essentially determined by the rainbow scattering. The deep well region features a maximal depth of almost-equal-to 300 meV and is associated with the backward glory. The well depths are in excellent to fair agreement with recent ab initio results.