Measurements of Excited Metastable Atoms and Ground State Atoms in a Nonequilibrium Heated Plasma Flow Reactor

Time-resolved, absolute populations of metastable atoms, N(2D,2P), and ground state atoms, N(4S) and O(3P), are measured in nitrogen and in a 1000 ppm NO-N2 mixture diluted in Ar, in a heated plasma flow reactor, at T=300-800 K. The flow in the reactor is excited by the ns pulse discharge bursts operated at a high pulse repetition rate, 100 kHz, generating a diffuse plasma with well-defined boundaries. The atomic species in the main ns pulse discharge are measured by the Atomic Resonance Absorption Spectroscopy (ARAS), using the vacuum UV emission produced by a probe discharge, operating at the same conditions. The results are corrected for the self-absorption of the incident resonance radiation in the probe discharge, before it is absorbed in the main discharge. No metastable O(1D) or O(1S) atoms have been detected. The focus of the future work is the verification of the ARAS data using the broadband VUV absorption spectroscopy, calibrated in inert gas mixtures (Xe and Kr), and measurements of NO+ ions, by mid-IR Cavity Ring Down Spectroscopy, to infer the rates of associative ionization in collisions of excited metastable atoms in the afterglow.