Experimental and Numerical Investigation of the Dependency of Reaction Dynamics on the Plasma Gas Temperature in He/N$_{2}$ Cryoplasmas

The plasma gas temperature ($T_{\mathrm{g}})$ is one of the essential parameters in plasma science and technology, but so far, the effect of $T_{\mathrm{g}}$ on low-temperature high-gas-density plasma chemistry has not been investigated in detail yet. Cryoplasmas, which are defined as plasmas whose $T_{\mathrm{g}}$ can be controlled below room temperature (RT), have the potential for various applications. In this study, to investigate the effect of $T_{\mathrm{g}}$ on the reaction dynamics in He/N$_{2}$ cryoplasmas, we developed a new 0D reaction model and also investigated the cryoplasmas by time-resolved laser absorption spectroscopy (LAS) and optical emission spectroscopy (OES). LAS measurements in He cryoplasmas at the same gas density as at RT and 1 atm, showed a longer lifetime (\textgreater 50 times) of metastable helium atom (He$^{\mathrm{m}})$ at cryogenic temperature (CT) compared to those at RT. OES revealed a time delay of the N$_{2}^{+}$ emission peak relative to the He emission peak of a few microseconds, and the delay decreased with increasing $T_{\mathrm{g}}$. The simulation using our reaction model suggested that the long lifetime of He$^{\mathrm{m}}$ at CT are due to the change of the reaction dynamics related to He$^{\mathrm{m}}$ as a function of $T_{\mathrm{g}}$.