Radiative transfer of a molecular S2B X spectrum using semiclassical and quantum-mechanical radiation coefficients

A fast method is presented for calculating the net emitted spectrum of a spherical sulphur plasma, from which the bulk of the radiation originates in the S 2 B 3 Σ u − → X 3 Σ g − molecular transition. The radiative transfer calculation needs as input the local spectral emission and absorption coefficients of the transitions. Calculations are presented using both a quantum-mechanical (QM) and a semiclassical (SC) method for generating these coefficients. It is found that the fine structure of QM coefficients, which is absent in the smooth SC data, may have a profound influence on the transport calculation. The circumstances where this occurs are identified and discussed. Measured spectra of the sulphur lamp are presented and compared with calculations, and a number of differences are found which may be due to an incorrectly modelled temperature profile or non-local thermal equilibrium (LTE) effects.