VUV photoabsorption spectroscopy of sulphur dioxide in the 1400–1600 Å region: Vibronic analysis of the [formula omitted] system

Abstract

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 ˜ A 1 1 → 3 A 1 1 , X ˜ A 1 1 → 2 A 2 1 and X ˜ A 1 1 → 2 B 1 1 . The observed vibrational features are found to be mainly due to excitation of the combination modes ( ν 1+ ν 2) and ( ν 2+ ν 3) with some contributions from ν 1 and ν 3. Details of the experiment and analysis are discussed in this paper.