STATE-RESOLVED STUDIES OF THE LASER-INDUCED DESORPTION OF NO FROM SI(111) 7X7 - LOW COVERAGE RESULTS

The results of a quantum-state-resolved study of the laser-induced desorption (LID) of NO from Si(111) 7 x 7 at a surface temperature of 100 K are reported. All aspects of the LID are found to be sensitive to the initial coverage. The coverage dependence indicates that there are two desorption mechanisms, one operative at low coverages that is quenched with increasing NO exposure, and one operative at high coverage. This report characterizes the low coverage channel. Most of the energy in the desorbed NO occurs as vibration and translation, with the rotations substantially cooler. The desorption is selective for production of the ground spin-orbit state. The energy partitioning shows strikingly little change as the desorption-laser wavelength was varied from 1907 to 355 nm. This, coupled with a quantitative study of the yield over the same photon energy range and selective coadsorption experiments, establishes that the desorption is specifically due to an interaction involving photogenerated holes in the rest-atom localized, intrinsic surface state of the 7 x 7 reconstructed surface. It is suggested that the surface state hole drives the desorption by neutralization of a NO-delta adsorbate.