Consequences of electronic-state mixing on the dynamics of photodissociation ofH2by barrier tunneling

The effect of electronic state mixing on tunneling dynamics is studied. To this aim the theoretical description of the differential photodissociation cross section is extended to include rotational and vibrational couplings. The mixing of bound and quasibound electronic states is reflected in resonance widths. The anisotropy of the photofragments reflects mixing of dissociative continua. It is shown that inclusion of these nonadiabatic couplings is required to reproduce the recently reported [Siebbeles, Schins, Los, and Glass-Maujean, Phys. Rev. A 44, 343 (1991)] differential photodissociation cross section of ${\mathrm{H}}_2$ for excitation around the ${\mathit{scri}}^3$ ${\mathrm{\Pi }}_{\mathit{g}}$ (v’=5, N’=1,2) resonances. Nonclassical photofragment anisotropies are found for coherent excitation of different rotational resonances (v’=5, N’=1, and N’=2) and of different rovibrational resonances (v’=5, N’=1 and v’=4, N’=2). The latter is strongly connected to the molecular excitation mechanism and has therefore no parallel in collision experiments.