NONADIABATIC RESPONSE TO SHORT INTENSE LASER-PULSES IN DISSOCIATION DYNAMICS

Molecular nonadiabatic response to the sudden switching on (rise times of few femtoseconds) of intense (tens of TW/cm(2)) laser pulses may l ead to some unexpected enhancements of dissociation rates. These effec ts are accounted for by the spreading of the molecule-plus-field wave packet over several resonances (instead of a single one predicted when the laser is adiabatically switched on) interfering during the excita tion process. Typical time-resolved signatures of such highly nonlinea r responses are thoroughly investigated in terms of the evolution of v ibrational survival probabilities and fragment kinetic energy spectra of H-2(+) molecular ion taken as an illustrative example. A plausible 532-nm wavelength single-photon dissociation scenario bringing into th e system less energy than the minimum required for the fragmentation t o occur is examined. The suggested mechanism, which may be termed belo w-threshold dissociation, as opposed to above-threshold dissociation, refers to a very sharp rise of the laser pulse resulting into temporal excitation of some resonances lying above the single-photon dissociat ion energy, with efficient decay rates.