High-resolution spectroscopy of molecular hydrogen in the extreme ultraviolet region

Abstract

We report high-resolution spectroscopy of the $D^{1}\ensuremath{\Pi}_{u}$, ${D}^{\ensuremath{'}\ensuremath{'}}^{1}\ensuremath{\Pi}_{u}$, and ${B}^{\ensuremath{'}\ensuremath{'}}^{1}\ensuremath{\Sigma}_{u}^{+}$ states in ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$, performed in absorption in the vicinity of 83 nm. Predissociative widths as narrow as 0.3 ${\mathrm{cm}}^{\ensuremath{-}1}$ have been measured, and profile analyses based on the theory of Fano are performed on these predissociated states. The importance of overlap integrals in the predissociation of ${B}^{\ensuremath{'}\ensuremath{'}}$ is shown, and the absorption cross section $\ensuremath{\sigma}=(7.2\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ for the ${B}^{\ensuremath{'}\ensuremath{'}}\ensuremath{\leftarrow}X(2,0)$ is determined. Anomalous behavior observed in the $D(v=5)$ states of ${\mathrm{D}}_{2}$ is analyzed in terms of an accidental perturbation by the ${D}^{\ensuremath{'}\ensuremath{'}}(v=0)$ states.