Scattering of H2 by LiF(001) studied using a new model potential. I. Prediction of large differences in diffraction of cold beams of para-H2 and normal-H2

Abstract

The close-coupling wave packet (CCWP) method has been used for performing calculations on rotationally and diffractionally inelastic scattering of H2 from LiF(001), using a model potential. The scattering from the initial j=0, 1, and 2 states was investigated at normal incidence for a collision energy of 0.1 eV. If the quadrupole-ionic lattice interaction is included in the potential model, large probabilities (up to 0.3) are obtained for reorientational (mj changing) transitions in the scattering from the initial j=1 and j=2 states. This is in contrast with results of previous theoretical work which used model potentials not including the electrostatic interaction and found much smaller probabilities for Δmj transitions. Inclusion of the quadrupole-ionic lattice interaction in the model also leads to the prediction of large differences between the diffraction of H2 in its j=0 rotational state and diffraction of j=1 H2. It should be possible to check this result by diffraction experiments employing cold beams of para-H2 and normal-H2. In addition, the calculations show large differences between the diffraction of ‘‘helicoptering’’ H2 (j=1 or 2, ‖mj‖=j) and ‘‘cartwheeling’’ H2 (j=1 or 2, ‖mj‖=0).