Knowledge Bank

The $\nu 1+\nu 3$ combination band is the strongest absorption band of $SO2$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">34</mrow>}SO2$ 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 $(\pm 0.00011cm-1)$. 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 $cm-2atm-1$ at 296 K for $\mathrm{<mrow\; data-mjx-texclass="ORD">32</mrow>}SO2$ 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 $0.11cm-1$ using NIST primary standard gas mixtures of $SO2$ in $N2$ with a total pressure of 1 atm. Nine measurements were made using a variety of partial pressures of $SO2$ and path lengths. The total integrated intensity obtained was $15.19(46)cm-2atm-1$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">32</mrow>}SO2$ of $13.31(40)cm-2atm-1$ was obtained in excellent agreement with the high resolution results.