UM: Measurements of atoms and metastable species in N2and H2-N2Ns pulse plasmas

Article

Abstract

Tunable Diode Laser Absorption Spectroscopy (TDLAS) and Two-photon Absorption Laser-Induced Fluorescence (TALIF) have been used to measure time-resolved, absolute densities of metastable N2(A3Σu+,v=0,1) molecules, ground state N and H atoms, and the rotational-translational temperature in diffuse N2 and N2-H2 plasmas during and after nanosecond pulse discharge bursts. These measurements, alongside kinetic modeling, reveal a significant decrease in N2(A3Σu+) populations and N atom generation rates during the bursts, suggesting a link between these trends. The slow decay of N atoms in the afterglow indicates that this trend persists beyond the discharge burst, unaffected by recombination or diffusion processes. This suggests that energy pooling in N2(A3Σu+) molecule collisions plays a crucial role in nitrogen dissociation in electric discharges. Further measurements in a 1% H2-N2 mixture show even greater reductions in N2(A3Σu+,v=0,1) populations, attributed to rapid quenching by accumulating H atoms, and a decrease in the N atom generation rate. However, the rate of H atom generation, mainly through dissociative quenching of excited nitrogen states by H2, remains consistent, leading to a steady increase in H atom density. These results, compared with kinetic models, highlight the complexity of atomic yield dynamics in H2-N2 plasmas, offering insights into their potential for applications like plasma-assisted ammonia synthesis.