Measured Shock-Layer Vibrational Populations and Temperatures in Arcjet Nitrogen Flow

Abstract

Radiation is analyzed from a highly nonequilibrium shock layer produced by a blunt body in a low-density arcjet now of nitrogen. Populations of vibrational states are obtained at several locations in the shock layer through fits of basis spectra to measured spectra. Several techniques determine the rotational and vibrational temperature corresponding to Boltzmann fits to low vibrational state populations for N 2 and N + 2 molecules. These techniques include correlations of ratios of intensity integrals, fits of calculated vibrational basis sets to measurements, and minimization of the deviation between calculated and measured spectra. Analyses of basis set fits yield vibrational populations that deviate from a Boltzmann distribution at vibrational quantum numbers greater than about 6-8. Differences in rotational and vibrational temperatures are found, together with temperature differences between the neutral molecule and the ion. Temperature profiles and non-Boltzmann vibrational populations indicate the nonequilibrium character of the layer. Experimentally determined population distributions should interest anyone modeling nonequilibrium vibrational kinetics. These distributions, up to v' = 20, should be of interest, and temperature profiles generally should be useful when validating the gas models used for high-enthalpy nonequilibrium nitrogen flows.