Dynamic Coupling Phenomena in Molecular Excited States. II. Autoionization and Predissociation in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>, Hd, and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">D</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

Vibrationally induced autoionization and one class of predissociation of electronically excited ${\mathrm{H}}_{2}$ and its isotopes are treated by a perturbed-stationary-state theory. Autoionization and predissociation rates are given for a number of states of ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$. In addition to direct bound-continuum coupling, consideration is given to effects of higher-order coupling; these effects cause order-of-magnitude changes in isolated cases. The auto-ionization rates vary with principal quantum number $n$ as ${n}^{\ensuremath{-}3}$, directly with vibrational energy $\mathrm{vh}\ensuremath{\nu}$, and decrease sharply with vibrational quantum change $\ensuremath{\Delta}v$. As the principal quantum number increases, transitions of successively smaller $\ensuremath{\Delta}v$ become possible; the net effect of this is to override the ${n}^{\ensuremath{-}3}$ dependence in total autoionization rates. Competition between predissociation and autoionization is examined; the two processes show very different dependence on $n$ and $v$, with the consequence that decay in most regions of ($n, v$) space is dominated by one or the other process; but the two mechanisms are competitive for some ($n, v$) states. The isotope effect also is rather different for the two decay processes, enough so that, in effect, the isotope effect amounts to a qualitative change from one mechanism of decay to the other, with mass change.