ROTATIONAL RAINBOWS IN THE INELASTIC-SCATTERING OF N2 FROM AU(111)

Resonantly enhanced multi-photon ionization (REMPI) laser spectroscopic and molecular beam-surface scattering techniques are coupled to study the rotationally inelastic scattering of N2 from Au(111). The scattered N2 rotational distributions are markedly non-Boltzmann and exhibit pronounced maxima at large angular momentum transfers (DELTA-J = 20 to 30). These maxima are indicative of direct rotational rainbow scattering and strongly depend upon the translational energy of the incident N2 molecular beam. The translational energy dependence of the rainbow rotational energy yields a value of 4.1 kcal mol-1 for the depth of the laterally averaged N2-Au(111) physisorption potential.