SPECTRAL WIDTHS OF H-2(-PULSES() MULTIPHOTON DISSOCIATION WITH SHORT INTENSE LASER)

Photodissociation spectra of H-2(+), Obtained using ultrashort (a few femtoseconds), intense (within the range of 10(12) to 10(14) W/cm(2)) laser pulses (with a peak frequency of 3.761 eV), and displaying well- separated proton kinetic-energy peaks corresponding to one-, two-, or three-photon absorptions are analyzed. Within some approximations, the validity range of which is related to the aforementioned assumptions on the laser and spectrum characteristics, a simple analytic formula i s deduced. It gives the spectral widths of the observed peaks in terms of the total number of photons which are absorbed and/or emitted duri ng the dissociation process. A quantitative support to some recent dyn amical interpretations is provided. The successive absorption of three photons seems basically to be the initial step which, at intermediate intensities, leads to the three-photon peaks. A subsequent emission o f one (or two) photons is responsible for the two- (or one-) photon pe aks. Bond softening occurs at higher intensities by the lowering of po tential-energy barriers. Dissociation proceeds through these barriers by reflection and tunneling. It involves at least three photons to end in a one-photon peak.