VUV photoabsorption spectroscopy of sulphur dioxide in the 1400-1600 Å region: Vibronic analysis of the (E)over-tilde-(X)over-tilde system

Gas phase photoabsorption studies of sulphur dioxide are carried out in the vacuum ultraviolet region using synchrotron radiation. Vibronic Analysis of the g system lying in the region 1400-1600 angstrom 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 similar to 1750 and similar to 1000 cm(-1). Results of the ab initio calculations suggest that at least three dominant excitations are involved in the (E) over tilde-(X) over tilde system viz. (X) over tilde (1)A(1) -> 3(1)A(1), (X) over tilde (1) -> 2(1)A(2) and (X) over tilde (1)A(1) -> 2(1)B(1). The observed vibrational features are found to be mainly due to excitation of the combination modes (v(1) + v(2)) and (v(2)+ v(3)) with some contributions from v(1) and v(3). Details of the experiment and analysis are discussed in this paper. (C) 2011 Elsevier Ltd. All rights reserved.