Double-resonance study of predissociation of the ${\mathit{j}}^3$${\mathrm{\Delta }}_{\mathit{g}}$ state of ${\mathrm{H}}_2$

A photoionization-photodissociation double-resonance technique has been employed to excite transitions from selected rovibrational levels of the metastable c ${}_{}{}^3{}_{}{}^{}\Pi _u^{\mathrm{-}}{}_{}{}^{}$ state to the rapidly predissociated j ${}_{}{}^3{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ state of ${\mathrm{H}}_2$. The photodissociation resonances arise from the configuration interaction between the j ${}_{}{}^3{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ and i ${}_{}{}^3{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ states, and exhibit the asymmetry of Fano-Beutler profiles. These resonances have widths that decrease with increasing v’ from 29 to 10 ${\mathrm{cm}}^{\mathrm{-}1}$; calculated predissociation widths show the same vibrational trend but are consistently 30% smaller. Results have been obtained for the rovibrational energy spacings of high-v levels within each state, and are in good agreement with theory. Photon energies for the c-to-j state transitions are slightly larger than those predicted theoretically.