Modelling the spectrum of a S/sub 2/ high pressure discharge

Summary form only given. High power microwave discharges in S/sub 2/ vapour at pressures of several bars have been discovered previously as a highly efficient white light source. The discharge spectrum is originating mainly from bound-bound transitions in the S/sub 2/ B/sup 3//spl Sigma//sub u//sup -/-X/sup 3//spl Sigma//sub g//sup -/ band system. At such high S/sub 2/ pressures re-absorption is an essential mechanism shifting the spectral maximum from the UV into the visible region. Assuming spherical symmetry, local thermal equilibrium and a cubic temperature profile the one-dimensional radiation transport equation is solved for each of the 330 vibronic bands connecting the niveaus /spl nu/´=0...9 and /spl nu/´´=0...32 yielding a quantitative description of the spectrum with only two free parameters: the maximum discharge temperature T/sub max/ and the mean width /spl delta//spl nu//sub vib/ of a vibronic band. The response of the spectrum to variations of experimental conditions (S/sub 2/ pressure, input power, ...) may be expressed by very reasonable changes of these model parameters: The input power determines the total amount of radiation (via the value of T/sub max/) and the S/sub 2/ pressure influences the position of the spectral maximum (reflected by the value of /spl delta//spl nu//sub vib/). In the red and IR the experimental spectrum is higher than the simulation indicating contributions of continuum radiation or other molecular transitions which are not included in the model.