Ternary recombination of H$_{3}^{+}$, H$_{2}$D$^{+}$, HD$_{2}^{+}$, and D$_{3}^{+}$ with electrons in He/Ar/H$_{2}$/D$_{2}$ gas mixtures

The temperature dependence of the ternary recombination rate coefficients of H$_{2}$D$^{+}$ and HD$_{2}^{+}$ ions has been studied in the temperature range of 80--150 K at pressures from 500 to 1700 Pa in a stationary afterglow apparatus equipped with a cavity ring-down spectrometer. Neutral gas mixtures consisting of He/Ar/H$_{2}$/D$_{2}$ (with typical number densities $10^{17}/10^{14}/10^{14}/10^{14}$ cm$^{-3}$) were employed to produce the desired ionic species and their fractional abundances were monitored as a function of helium pressure and the [D$_{2}$]/[H$_{2}$] ratio of the neutral gas. In addition, the translational and the rotational temperature and the ortho to para ratio were monitored for both H$_{2}$D$^{+}$ and HD$_{2}^{+}$ ions. A fairly strong pressure dependence of the effective recombination rate coefficient was observed for both ion species, leading to ternary recombination rate coefficients close to those previously found for (helium assisted) ternary recombination of H$_{3}^{+}$ and D$_{3}^{+}$.\footnote{R. Johnsen \textit{et al.}, J. Phys. Chem. \textbf{117}, 9477 (2013).}