Desorption of Hydrogen from Si(111) by Resonant Excitation of the Si-H Vibrational Stretch Mode*

We report first measurements of non-thermal, non-electronic resonant photodesorption of hydrogen from a Si(111) surface using tunable infrared radiation. The wavelength dependence of the desorption yield Shows a peak at 0.26 eV, the energy of the Si-H vibrational stretch mode. The corresponding excitation cross section is determined to be $2.3\times10^{-18}$ cm$^2$. The desorption yield is quadratic in the infrared intensity and quartic in the electric field along the Si-H bond direction. We postulate that two neighboring hydrogen adatoms, once simultaneously excited in their vibrational stretch mode, can desorb associatively at room temperature.