Knowledge Bank

The optogalvanic spectra of the highly excited $H2$ and $D2$ by de discharge have been investigated. Five bands of the triplet systems were observed in the $16200-17400cm-1$ region; from $c3\pi 3$ to $h3\Sigma g+,g3\Sigma g+,i3\pi g$, and $h3\Delta g$ and from $h3\Sigma g+$ to $d3\pi u$ transitions. Comparing the optogalvanic spectra with the ordinary emission spectra of $H2$ and $D2$, in the case of $H2$ the half of the optogalvanic transitions from $c3\pi u$ state was weak or missing. This fact confirmed that the $c3\pi u+$ state of $H2$ predissociated into the repulsive state $b3\Sigma u+$. However, in the case of $D2$ many optogalvanic transitions from $c3\pi u+$ state were observed. The calculation of Comtet and $Bruijn1$ demonstrated that the predissociative lifetime of the $c3\pi u\ast$ state in $D2$ was much longer than that in $H2$. The observation of many optogalvanic transitions in $D2$ is explained as a long predissociative lifetime in $D2$. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ G. Comtet and D. P. de Bruijn, Chem. Phys. 94 365 (1985).