ENERGY-RESOLVED ANGULAR-DISTRIBUTIONS AND THE POPULATION PARTITION OFEXCITED-STATE RH ATOMS EJECTED FROM ION-BOMBARDED RH-(001)

The energy-resolved angular distributions of Rh atoms ejected from Rh {001} by bombardment with 5.0 keV Ar+ ions have been measured for the ground state (a F-4(9/2)) and the two lowest lying excited state (a F- 4(7/2),a F-4(5/2)). Simultaneous measurements on these electronic stat es provide us an opportunity to examine the influence of electronic in teractions on desorbed particles. The experimental results show that t here is a sequential variation in the angular distributions as the exc itation energy increases. These variations are attributed to the inter action between the substrate electrons and the excited state atom as i t is being ejected from the surface. Since the measurements are perfor med using multiphoton ionization via a single intermediate state, the population partition among the three lowest states is obtained as well . The excitation probabilities of the a F-4(7/2) and F-4(5/2) states a re compared with those predicted from the expression exp(-A/av(1)) and with a recently proposed model involving interatomic collisions above the surface. Results suggest that atoms excited via this mechanism ma ke a significant contribution to the population of atoms ejected with low ejection velocities for the first-excited a F-4(7/2) state (0.19 e V), as reported previously. Moreover, we suggest that an even higher p roportion of atoms in the a F-4(5/2) state are produced via this mecha nism.