High-resolution spectroscopy of SO2 using a frequency-doubled, continuous-wave dye laser

The SO2 molecule is of considerable interest in the context of atmospheric pollution, and in many laser monitoring techniques the ultraviolet absorption band at 300 nm is used to determine SO2 concentrations in the atmosphere. Recent laboratory experiments with a resolution of 2 x 10 to the -3rd nm showed that variations could occur in absorption cross-section measurements made with different laser bandwidths due to unresolved fine structure. Absorption spectra with a line width of 3 x 10 to the -6th nm, using a frequency-doubled continuous-wave dye laser were investigated, and the existence was confirmed of fine structure in the absorption even when collisionally broadened with an atmosphere of nitrogen. These measurements provide a data base from which valid absorption cross sections may be calculated for all monitoring laser bandwidths. The pressure broadening coefficient for nitrogen in this wavelength region was estimated as 83 + or - 38 kHz/Pa. The temperature dependence of the absorption cross section was also investigated.