Absorption measurements of sulfur vapor

Summary form only given, as follows. High intensity pure sulfur discharge lamps have recently attracted attention due their excellent lamp efficacy. The observed emission spectrum originates from pressure broadened vibronic transitions of the S/sub 2/ molecule modified by self-absorption in the ultraviolet and blue spectral regions. No atomic lines from S(I) are found in the emission spectra. The absorption coefficients for S/sub 2/ and other sulfur molecules are needed to completely understand the mechanisms of radiation generation and transport in the plasma. Some data exist for S/sub 3/ and S/sub 4/, however no absolute absorption cross sections are reported for S/sub 2/. We have measured the absorption cross section of dilute sulfur vapor at various temperatures (700/spl deg/C-1000/spl deg/C) and pressures (26-270 mbar) using a broad band light source. Under these conditions the vapor consists mainly of S/sub 2/ with only a small fraction of larger molecules (S/sub 3/..S/sub 8/). Vibrational transitions of S/sub 2/:X/sup 3//spl Sigma//sub g/-B/sup 3//spl Sigma//sub u/ (v´´, v´) with v´´=0...6 and v´=0...7 were identified. The absorption cross sections correspond to Franck Condon factors reported for the transitions and vary between 10/sup -/17 cm/sup 2/ at 280 nm and 2/spl middot/10/sup -/19 cm/sup 2/ at 380 nm. Significant absorption due to S/sub 3/ was observed in the spectral region from 350 to 450 nm. This occurs especially at increased sulfur pressures and lower temperatures (700/spl deg/C). The absorption cross sections determined for S/sub 3/ were higher than for S/sub 2/ and in agreement with published data. These data support the hypothesis that the emission spectrum of the high intensity sulfur lamp is shaped by self absorption of S/sub 2/ in the high temperature zone of discharge and absorption of S/sub 3/ in the cooler mantle near the wall.