THEORY OF DESORPTION INDUCED BY ELECTRONIC-TRANSITIONS .2. THE STRONGINTERACTION REGIME

The dynamics of desorption induced by electronic transitions is studie d using a recently formulated quantum mechanical method [J. Chem. Phys . 106, 417 (1997)]. We consider two qualitatively different model Hami ltonians representing the limits of desorption induced by a single and by multiple electronic transitions and at the same time the limits of resonance-mediated and direct nuclear dynamics. The photodesorption p robability of NH3/Cu induced by low-intensity, nanosecond pulses is do minated by a resonant component and determined by the competition of d esorption with vibrational relaxation. The probability is linear in th e excitation intensity but highly nonlinear in the nonradiative coupli ng. The photodesorption of NO/Pd induced by intense, femtosecond pulse s involves complex electronic dynamics and its vibrational dynamics is mostly direct. Multiple transitions to an ionic state are shown forma lly and numerically. These give rise to several thresholds in the time -resolved desorption probability. A power-law fluence dependence is fo und, consistent with observations. (C) 1997 American Institute of Phys ics. [S0021-9606(97)01244-0].