Radiation code SPRADIAN07 and its applications

Abstract

A new radiation code SPRADIAN07 has been developed by using the line-by-line technique for bound-bound transitions and absorption cross sections for bound-free and free-free transitions. This code contains the latest spectroscopic constants and electronic vibrational transition moments. SPRADIAN07 is capable of calculating both Boltzmann and non-Boltzmann radiations. Especially, under non-Boltzmann excitation, a master equation is solved to determine the extent of the departure from the Boltzmann distribution by assuming that the internal states are distributed according to the quasi-steady-state (QSS) condition. For the calculation of non-Boltzmann effects in diatomic systems, the state-to-state transitions due to collisions of heavy particles and electrons are accounted for. Molecular diatomic symmetries such as spin-orbit splitting and lambda splitting are studied. The six subroutines are constructed corresponding to different Hund’s cases, i.e., electronic states and their spin multiplicities, to treat spin-orbit splitting phenomena. This results in more accurate rotational line strength (H$\ddot{o}$nl-London) factors and accordingly accurate spectral line locations. Lambda splitting is partially completed only for spin doublet to doublet transitions. Three applications are studied with the use of SPRADIAN07: 1) CN radiation measured in shock tube experiments performed by the KAIST group, Marseille University group, and NASA Ames Research Center group; 2) NO spectra obtained by the NASA Ames group and the Kyushu University group in arcjet flows; and 3) CH spectrum scheduled to be measured in the near future. SPRADIAN07 accurately reproduces CN Violet radiation measured by the KAIST group under Boltzmann excitation. The radiation data of CN Violet and CN Red obtained by the Marseille University group and NASA Ames group seemed to come from weakly and strongly non-Boltzmann distributions. We employs two models to explain such CN Violet and CN Red radiat...