Theory of desorption induced by electronic transitions. II. The strong interaction regime

The dynamics of desorption induced by electronic transitions is studied using a recently formulated quantum mechanical method [J. Chem. Phys. 106, 417 (1997)]. We consider two qualitatively different model Hamiltonians 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 probability of NH₃/Cu induced by low-intensity, nanosecond pulses is dominated by a resonant component and determined by the competition of desorption with vibrational relaxation. The probability is linear in the excitation intensity but highly nonlinear in the nonradiative coupling. The photodesorption of NO/Pd induced by intense, femtosecond pulses involves complex electronic dynamics and its vibrational dynamics is mostly direct. Multiple transitions to an ionic state are shown formally and numerically. These give rise to several thresholds in the time-resolved desorption probability. A power-law fluence dependence is found, consistent with observations.