Moderate Dispersion Spectra of NH2 in Comet Hale-Bopp: Analysis of Population Distribution in $\widetilde X^{2} \textrm B_{1}(0,0,0)$ State of NH 2

Abstract

Abstract We carried out moderate-dispersion spectroscopic observations of comet Hale-Bopp (C/1995O1) on 1997 February 25, in order to study the fine structure of two NH 2 emission bands, $\widetilde A(0,9,0)-\widetilde X(0,0,0)$ and $\widetilde A(0,8,0)-\widetilde X(0,0,0)$ , which was resolved in our spectra. We compared the observed fine structure with that of the modeled spectra, which were computed based on the transition probabilities of NH 2 between the $\widetilde A(0,v^{\prime}_{2},0)$ and $\widetilde X(0,0,0)$ states determined by ourselves. From a comparison between the observation and the calculations we concluded that the population distribution of the NH 2 in the $\widetilde X(0,0,0)$ ground state can be approximated by the Boltzmann distribution at a temperature of 60 K.