The experimental spectrum of the (G) 3 (A) 0 (SA) 2 cluster along with the lowest energy calculated spectra are shown in the Figure . A direct comparison to the (G) 2 (A) 0 (SA) 1 spectrum allows us to obtain some qualitative information of the structure. In the experimental spectrum, the carbonyl stretching mode is partially resolved into peaks centered at 1781 cm -1 and 1768 cm -1 , with a small shoulder at 1739 cm -1 . The observed splitting is characteristic of all three carbonyls being involved in hydrogen bonding, with the degree of splitting a direct indication of the local hydrogen bonding environments of each carbonyl group. Below 1730 cm -1 , the S-OH stretch and the SO 3 symmetric stretch are the most notable features in the spectrum. All other transitions are rather diffuse and limit our ability to extract structural information solely from the experimental spectrum.