Rydberg states of triatomic hydrogen and deuterium*

Triatomic hydrogen ($\rm{H_3}$) and its isotopologue ($\rm{D_3} $) are the simplest neutral polyatomic molecules. They have been of great interest in recent decades. In a previous study [1], we calculated radiative transitions between neutral $\rm {H_3}$ Rydberg states and described the mid-infrared laser lines observed in hydrogen/rare gas discharges. We extend the study to $\rm{D_3}$, and discuss the mechanism for the population inversion that is required for lasing action, which has been observed by the Berkeley group.\\[4pt] [1] R. J. Saykally, E. A. Michael, J. Wang, and Chris H. Greene, J. Chem. Phys. \textbf{133}, 234302 (2010).