The wavelength dependence of photoinduced hot electron dissociative attachment to methyl bromide adsorbed on gallium arsenide (110)
- Columbia Radiation Laboratory, Columbia University, New York, New York 10027 (United States)
The wavelength dependence of photoinduced dissociation of CH{sub 3}Br via dissociative electron attachment (DEA) of {open_quotes}hot{close_quotes} electrons for one monolayer CH{sub 3}Br adsorbed on GaAs(110) has been measured. The cross section for dissociation is found to decrease monotonically by two orders of magnitude as the incident wavelength is varied from 308 to 550 nm. There is an apparent threshold near 490 nm (2.5 eV), well below the gas phase photodissociation threshold near 250 nm (5.0 eV), but in good agreement with a simple estimate based on expected values for the decrease in the photoemission threshold and the lowering of the molecular affinity level upon adsorption of CH{sub 3}Br on a semiconductor surface. The observed threshold is found to move to higher energy as dissociation of the monolayer proceeds. Based on the work of Hasselbrink and co-workers [F. Weik, A. de Meijere, and E. Hasselbrink, J. Chem. Phys. {bold 99}, 682 (1993)], a simple theoretical model is developed which considers the tunneling of hot electrons through the interfacial barrier between the physisorbed CH{sub 3}Br and the GaAs. The results of our theoretical model in conjunction with those of earlier {ital ab initio} calculations [S. Black, R. Friesner, P. H. Lu, and R. M. Osgood, Jr., Surf. Sci. {bold 382}, 154 (1997)] suggest that the adsorbate affinity level is centered at {approximately}0.6 eV above the (adsorbate- modified) vacuum level of the substrate. This value corresponds to a {approximately}1.8 eV stabilization of the negative ion resonance upon adsorption. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 663691
- Journal Information:
- Journal of Chemical Physics, Vol. 109, Issue 18; Other Information: PBD: Nov 1998
- Country of Publication:
- United States
- Language:
- English
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