INTERNAL-STATE DISTRIBUTIONS OF H-2 DESORBED FROM MONOHYDRIDE AND DIHYDRIDE SPECIES ON SI(100)

Following adsorption of atomic hydrogen on Si(100)-(2 X 1), the surface is heated and the desorbed H-2 is detected via (2 + 1) resonance-enhanced multiphoton ionization (REMPI). H-2 desorption correlated with the decomposition of dihydride groups on the surface (SiH2) is detected at a surface temperature T(s) near 660 K, and with the monohydride species (SiH) near T(s) = 780 K. Although the H-2 rotational distributions are nearly identical for the mono- and dihydride species, the vibrational distributions differ with roughly 0.2% and 1% of the population in H-2 (v = 1 for the monohydride and dihydride, respectively. The enhancement in the [H-2 (v = 1) ]/[H-2 (v = 0)] population ratio over that of a thermal distribution at T(s) is, however, roughly 20 times for both mono- and dihydride species. The results are interpreted within a model that assumes desorption proceeds through a common intermediate, which is identified as the dihydride.