Shock-Tube Study of Radiation from S2

Absolute emission intensity measurements of the radiation from sulfur molecules S₂ have been obtained in the temperature range from 2300 to 4800°K at six wavelengths spaced between 3132 and 5461 Å. The radiation intensities were proportional to the square of the sulfur atom concentration and were independent of the total pressure of the buffer gas, argon. In addition, the band structure was recorded for the wavelength interval 3600–4100 Å with an image orthicon camera mounted in a spectrograph. The intensities between 3650 and 5461 Å have similar activation energies and are interpreted in terms of the radiative transitions from the $B^3{\Sigma }_u^{-}$ state of molecular sulfur, this state being populated by the mechanism of inverse predissociation. Theoretical calculations of the $B^3{\Sigma }_u^{-}$ bands predicted the band shapes observed with the image orthicon and, together with the measured intensities, provide the electronic $f$ value for the bands. The square of the transition moment ${\mathrm{[Re(r)\hspace{0.17em}/\hspace{0.17em}ea}}_0{]}^2$ is estimated to have a value of 5.0, which corresponds to an $f$ value of 0.16 on the basis of published Franck–Condon factors. The intensities at 3132 Å have a temperature dependence close to that predicted for transitions from the $b^1{\Delta }_u$ electronic state.