Photodesorption of nitric oxide from Pt(111) using femtosecond laser pulses at 620 nm and 310 nm is found to result in a superlinear dependence of desorption yield on absorbed laser fluence. The translational energy distributions of the desorbed molecules are found to be nearly Maxwell-Boltzmann. For both 620 nm and 310 nm pulses with adsorbed fluences greater than 2.5 mJ/cm2, the average translational energy is found to increase linearly. At lower fluences, it is constant at 750 K, possibly suggesting a transition between DIMET and DIET desorption processes. In two pulse correlation measurements, it is found that the first pulse yield and the average translational energy have different widths as a function of delay between pulses.
This paper reviews our understanding on the dynamics of vibrational heating and bond- breaking within a universal electronic mechanism, i.e. the multiple scattering mechanism induced by hot-electrons generated by femtosecond laser pulses. A few theoretical approaches, based on the reduced density matrix and a resonance model of electron-molecule coupling, are briefly sketched and discussed, and qualitative features of vibrational heating and bond- breaking are emphasized. Two illustrative examples of vibrational heating of CO stretch on Cu and O2 desorption from Pt(111) demonstrate that the dynamics of electronic and vibrational heating can be partly revealed by the yield and final state distribution analysis.
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