Absorption intensities of zero-phonon double transitions involvingpara−H2–ortho−H2pairs in solid hydrogen

Abstract

The infrared spectrum of solid ${\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\ensuremath{-}\mathrm{H}}_{2}$ containing ${\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\ensuremath{-}\mathrm{H}}_{2}$ at trace level shows relatively weak features due to zero-phonon double transitions involving ${\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\ensuremath{-}\mathrm{H}}_{2}{--\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\ensuremath{-}\mathrm{H}}_{2}$ pairs. Formulas are developed for the intensities of such double transitions and the theoretical results compared with experimental findings.