Coherent elastic and rotationally inelastic scattering of N-2, O-2, and CH4 from a 10 K Cu(111) surface

We report observations of coherent elastic and rotationally inelastic scatt ering of N-2, O-2, and CH4 from a 10 K Cu(111) surface, kept clean by pulse d laser heating. The related sharp features in the measured angular distrib utions decrease drastically in intensity at elevated target temperatures. A t low temperature rotational transitions reduce the elastic scattering prob ability by about an order of magnitude. This effect is weak for D-2 at the impact conditions of concern. Quantum scattering calculations for N-2 and D -2 show that this difference is primarily caused by the large difference in rotational constants and the associated rotational transition energies of these molecules. (C) 2000 American Institute of Physics. [S0021-9606(00)703 44-8].