Knowledge Bank

In 1993, we reported observations of the infrared absorption spectra of $D3$ with a difference frequency laser system in the frequency ranges around $3600cm-1(3s2A1\prime \leftarrow 3p2E\prime )$ and $3900cm-1(3d\leftarrow 3p2E\prime )a$. The observed line shapes exhibited a board non-Maxwellian velocity distribution, and the line shapes depended on the rotational states. At that time, the line shapes and the widths were not completely understood. Here we present a more detailed and consistent analysis. Most lines of the $3600cm-1$ band appear to be a superposition of two components, broader and narrower features, for some transitions with an opposite phase. From a broader flat-topped line profile, it is concluded that $D3$ carries excess translational energy of 0.4 eV and is formed through the dissociative recombination reaction of $D5+$ with electrons. The rotational dependence of the line shapes of the $3600cm-1$ band is brought about by a competition between the predissociation in the $3s2A1\prime$ state and the radiative decay in the $3p2E\prime$ state. The shorter lifetimes of the 3d complex make the line shape of the $3900cm-1$ band simpler, a superposition of two absorption profiles with different widths. It is found that the widths of the lines of the $3900cm-1$ band are larger than those for the $3600cm-1$ band lines. The greater widths of the $3900cm-1$ band are attributed to unresolved spin-splittings. Attempts to observe similar absorption lines of $H3$ were unsuccessful, presumably due to much shorter lifetimes.