COMPARISON OF THE $\nu_{1} + \nu_{3}$ BAND INTENSITY OF $SO_{2}$ DETERMINED BY HIGH RESOLUTION MEASUREMENTS AND THE TOTAL INTEGRATED BAND INTENSITY TECHNIQUE

Abstract

The $\nu_{1} + \nu_{3}$ combination band is the strongest absorption band of $SO_{2}$ that falls in an atmospheric window. We have studied this band with a difference-frequency laser spectrometer at low pressure (0.20 Torr - 8.25 m path) to minimize pressure broadening effects. Close to 2000 lines of the (101-000) and (111-010) bands have been assigned as well as 100 lines of the (101-000) band of the $^{34}SO_{2}$ isotopic species. After correction for a very weak Fermi interaction of the enery levels of (101) With the nearby (120) state, the observed transition wavenumbers can be fit using a Watson Hamiltonian to within the experimental uncertainty $(\pm 0.00011 cm^{-1})$. The observed peak absorptions together with small corrections for pressure broadening and instrumental effects were used to calculated individual line intensities for all unblended lines. These intensities were least-squares fit, and transition moments as well as their rotational corrections were obtained. These rotational and transition moment constants were then used to generate a listing of line positions and intensities, and the total band intensity was obtained by summing all the calculated intensities. The band intensities obtained in $cm^{-2} atm^{-1}$ at 296 K for ${^{32}}SO_{2}$ are $S_{\nu}(101-000) = 13.36, S_{\nu}(111-010) = 1.052$ and $S_{\nu}(120-000) = 0.170$. The uncertainty in these values is estimated to be $\pm 5%$. The total integrated band intensity was obtained using a commercial FT spectrometer at a resolution of $0.11 cm^{-1}$ using NIST primary standard gas mixtures of $SO_{2}$ in $N_{2}$ with a total pressure of 1 atm. Nine measurements were made using a variety of partial pressures of $SO_{2}$ and path lengths. The total integrated intensity obtained was $15.19(46) cm^{-2} atm^{-1}$ at 296 K. After correction for hot band contributions to the intensity and the isotopic abundance of sulfur, a value for the total band intensity of the (101-000) band of $^{32}SO_{2}$ of $13.31(40) cm^{-2} atm^{-1}$ was obtained in excellent agreement with the high resolution results.