Spectroscopic Determination of the Relative Concentrations of H2, HD, and D2 Molecules in Nonequilibrium Hydrogen-Deuterium Plasma: I. Kinetic Models

The possibility of estimating the relative concentrations of H-2, HD, and D-2 molecules in nonequilibrium low-pressure hydrogen-deuterium plasma from the observed relative intensities of spectral lines of atoms and molecules is examined. It is demonstrated that the intensity ratios of the Balmer lines of hydrogen and deuterium atoms can be used to estimate the relative concentrations of the isotopic molecules in two limiting cases, namely, a fairly high degree of dissociation of the molecules in plasma (model 1a) and a fairly low one (model 1b). A procedure is suggested for deriving the relative concentrations of H-2, HD, and D-2 molecules from the observed intensity ratios of Q-branch lines of Fulcher-a bands of these molecules within a simplified model of the excitation and deactivation of rovibronic levels (model 2). The procedures proposed here are fully independent, for they are based on consideration of different physical processes, use different experimental data, and do not involve any fitted parameters. Therefore, simultaneous use of the different independent models provides means to assess their applicability under particular experimental conditions.