ON THE LOW-ENERGY LIMITS OF INELASTIC MOLECULE-SURFACE SCATTERING

The zero energy scattering limit of inelastic molecule-surface scatter ing is studied within the context of a multiphonon expansion of the mo lecule-bath wave function. By assuming that at low scattering energies the expansion may be truncated at first order in the phonon operators , we derived a closed form solution to the Lippmann Schwinger equation for the scattering wave function which includes a nonlocal and energy dependent self-energy term which correctly incorporates virtual phono n transitions in the elastic channel. The closure relation results fro m the use of a discrete spectral (L2) form of the inelastic channel Gr eens functions. We compute the zero energy limit of these wave functio ns and discuss the trapping and reflection of cold atoms from ultracol d surfaces. Our results indicate that for realistic atom surface inter actions the low energy limit of the sticking coefficient, s, can devia te markedly from the expected s is-proportional-to E1/2 behavior and i s shown to approach a constant nonzero limiting value. This trend is c onsistent with recent experimental work involving the sticking of spin polarized hydrogen atoms on liquid He films.