Laser catalysis and transition state spectra of the H+H2 exchange reaction

Publisher Website
Google Scholar
Abstract
Electronic excitation ‘‘transition‐state’’ spectra of the H+H2 exchange reaction are computed by a uniform semiclassical approximation, at a number of collision energies. The spectra, which compare well with the coupled channels computations of Engel et al. [J. Chem. Phys. 8 2, 4844 (1985)] are shown to yield unique information pertaining to ultrashort time dynamics. The transition amplitudes are then incorporated in a general formulation by which the laser catalysis scheme, suggested recently by Shapiro and Zeiri [J. Chem. Phys. 8 5, 6449 (1986)] is treated exactly. According to this scheme, reaction barrier crossings can be achieved through resonant light scattering via a bound upper electronic state. The laser acts as a catalyst, since no net photons are absorbed or emitted. When the process is coherent, interference between ‘‘natural’’ (nonradiative) tunneling and the optical process is shown to lead to ‘‘Fano‐type’’ dependence of the reactive probabilities on laser frequency: The reaction is stopped on the red side and enhanced on the blue side of the absorption line. For an ensemble of reactants with thermal‐like distribution of kinetic energies, laser catalysis is shown to depend linearly on the laser power. For H+H2, the effect is most pronounced at threshold and subthreshold energies.