VUV photoabsorption spectroscopy of sulphur dioxide in the 1400-1600 à region: Vibronic analysis of the E˜−X˜ system

Gas phase photoabsorption studies of sulphur dioxide are carried out in the vacuum ultraviolet region using synchrotron radiation. Vibronic Analysis of the E˜−X˜ system lying in the region 1400-1600 Å is reported for the first time. A larger number of spectral features are resolved compared to earlier reports. While most of the observed bands can be arranged into four series with successive band spacing of 500-620 cm−1 in agreement with previous work, we observe two additional series with average separation of ∼1750 and ∼1000 cm−1. Results of the ab initio calculations suggest that at least three dominant excitations are involved in the E˜−X˜ system viz. X˜A11→3A11, X˜A11→2A21 and X˜A11→2B11. The observed vibrational features are found to be mainly due to excitation of the combination modes (ν1+ν2) and (ν2+ν3) with some contributions from ν1 and ν3. Details of the experiment and analysis are discussed in this paper.

► Photoabsorption spectra of SO2 (1400-1600 Å) using synchrotron radiation. ► Theoretical calculations on excited states of SO2 using the GAMESS code. ► Vibronic analysis of the E-X system using ab initio calculations. ► Possible excitations in the E˜−X˜ system dominated by X˜A11→3A11, X˜A11→2A21 and X˜A11→2B11. ► Observed features are due to excitation of (ν1+ν2), (ν2+ν3), ν1 and ν3.