Cross sections and angular distributions for individual fragment fine structure levels produced in one- and two-photon photodissociation of NaH

Close coupled calculations are presented for photodissociation of NaH to the first excited atomic limit NaH + hν→Na(²P _1/2,3/2) + H(²S). The calculations employ ab initio potential curves and dipole matrix elements. Resonances are predicted in the low energy photodissociation cross section to each of the sodium fine structure levels, and some are shown to arise from nonadiabatic interactions. The calculated ratio of the Na (²P_3/2) to the Na( ²P_1/2) cross section does not approach the predicted high energy limit of 2:1 until the excess dissociation energy is more than an order of magnitude larger than the atomic spin-orbit splitting. Anisotropy parameters, that describe the angular distribution of photofragments and polarized sodium D-line fluorescence, exhibit dramatic energy variation near threshold, including some resonance structure. In general, these anisotropy parameters are different for fragments produced in each of the sodium fine structure levels. These NaH calculations delineate some of the qualitative features to be anticipated in wide classes of diatomic photodissociation involving fragments with fine structure.