Isotope effect and gerade versus ungerade symmetry in HD predissociation revealed by theH(2s),H(2p),D(2s), andD(2p)fragments

Abstract

The isotope effect and the $g\ensuremath{-}u$ symmetry in the HD predissociation have been studied by detecting the $\mathrm{H}(2s)$, $\mathrm{H}(2p)$, $\mathrm{D}(2s)$, and $\mathrm{D}(2p)$ fragments. For transitions to the $3p\ensuremath{\pi}D{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}^{+}(\ensuremath{\upsilon}=4)$, $4p\ensuremath{\pi}{D}^{\ensuremath{'}}{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}^{+}(\ensuremath{\upsilon}=1)$, and $4p\ensuremath{\sigma}{B}^{\ensuremath{'}\ensuremath{'}}{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}(\ensuremath{\upsilon}=2)$ states of HD, the branching ratios of the four dissociation channels, $\mathrm{H}(2s)+\mathrm{D}(1s)$, $\mathrm{H}(2p)+\mathrm{D}(1s)$, $\mathrm{D}(2s)+\mathrm{H}(1s)$, and $\mathrm{D}(2p)+\mathrm{H}(1s)$, were measured. Strong asymmetric distributions are found between the $\mathrm{H}(2s)+\mathrm{D}(1s)$ and $\mathrm{D}(2s)+\mathrm{H}(1s)$, and between the $\mathrm{H}(2p)+\mathrm{D}(1s)$ and $\mathrm{D}(2p)+\mathrm{H}(1s)$ channels. The results indicate the existence of $g\ensuremath{-}u$ symmetry breaking as well as strong nonadiabatic couplings near the HD dissociation limits. However, the angular anisotropy parameters are found to be the same for the $\mathrm{H}(2s/2p)$ and $\mathrm{D}(2s/2p)$ fragments. In addition, the observed Beutler-Fano profiles in the $\mathrm{H}(2s/2p)$- and $\mathrm{D}(2s/2p)$-atom action spectra show no dependence on the H and D isotopes. This implies that the angular distribution of the fragments and the Beutler-Fano profiles are determined chiefly by the Franck-Condon transitions and are not affected by the $g\ensuremath{-}u$-state mixing.