Measurements of rate coefficients of CN$^+$, HCN$^+$ and HNC$^+$ collisions with H$_2$ at cryogenic temperatures

Abstract

The experimental determination of the reaction rate coefficients for production and destruction of $\text{HCN}^+$ and $\text{HNC}^+$ in collisions with $\text{H}_2$ is presented. A variable temperature 22 pole radio frequency ion trap was used to study the reactions in the temperature range of $17 - 250\;\text{K}$. The obtained rate coefficients for the reaction of $\text{CN}^+$ and of $\text{HCN}^+$ with $\text{H}_2$ are close to the collisional (Langevin) value, whereas that for the reaction of $\text{HNC}^+$ with $\text{H}_2$ is quickly decreasing with increasing temperature. The product branching ratios for the reaction of $\text{CN}^+$ with $\text{H}_2$ are also reported and show a notable decrease of $\text{HNC}^+$ product with respect to $\text{HCN}^+$ product with increasing temperature. These measurements have consequences for current astrochemical models of cyanide chemistry, in particular for the $\text{HCNH}^+$ cation.