Upon condensation of the pure planar gas SO3 (D3h) trimerizes spontaneously, which is often called γ-SO3. It adopts a cyclic structure (C3V) described as [S(=O)2(μ–O)]3. The highly electrophilic nature of γ-SO3 results in insertion reactions into M-C as well as M-O (M = Si, Ge, Sn, Pb) bonds under very mild conditions to leave the organic portion of the molecule intact [1-3]. Other experimental and theoretical investigations of γ-SO3 and its derivatives have been relatively sparse. Thus, the main objective of the present work is to study the trimerization of SO3 in the gas phase, with density functional theory (DFT) at the B3LYP/ 6-31G(d) basis set level. The basis set superposition error (BSSE) associated with the polymerization energy was computed via the counterpoise method using the individual bases as fragments [4]. DFT calculations were carried out to predict the structures and vibrational (Raman and infrared) spectra and were compared to the experimental results [5-7]. Theoretical calculations were also carried out for SO3 and γ-SO3 for better understanding the intermolecular interactions.

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