ENERGY-RESOLVED ANGULAR-DISTRIBUTIONS AND THE POPULATION PARTITION OF EXCITED-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 states provide us an opportunity to examine the influence of electronic interactions on desorbed particles. The experimental results show that there is a sequential variation in the angular distributions as the excitation energy increases. These variations are attributed to the interaction between the substrate electrons and the excited state atom as it is being ejected from the surface. Since the measurements are performed 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 are 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 make 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 eV), as reported previously. Moreover, we suggest that an even higher proportion of atoms in the a F-4(5/2) state are produced via this mechanism.