| Abstract
| - The preferred conformations of dimethyl sulfite and their vibrational spectra were studied by matrix-isolationFourier transform infrared spectroscopy and theoretical methods (density functional theory (DFT) and Moller−Plesset (MP2), with basis sets of different sizes, including the quadruple-ζ, aug-cc-pVQZ basis). Five minimawere found at these levels of theory. At the MP2/6-31++G(d,p) and DFT/B3LYP/aug-cc-pVQPZ levels, theGG conformer (where the O−S−O−C dihedral angles are 73.2 and 70.8°) resulted in the conformationalground state. At the highest level of theory used, the GT conformer (O−S−O−C = +68.5 and −173.2°) is0.83 kJ mol-1 higher in energy than the GG form, while conformer GG‘ (O−S−O−C = +85.7 and −85.7°)has a relative energy of 1.18 kJ mol-1. The remaining two conformers (G‘T and TT) are high-energy formsand not experimentally relevant. In consonance with the theoretical predictions, conformer GG was found tobe the most stable conformer in the gaseous phase as well as in the low-temperature matrices. Annealing ofthe argon matrices first promotes the GG‘→GT isomerization, which is followed by conversion of GT intothe most stable conformer. There is no evidence of occurrence of GG‘→GG direct conversion in the low-temperature matrices. On the other hand, during deposition of the xenon matrices conformer GG‘ totallyconverts to conformer GT. Two observations demonstrated this fact: no evidence of bands corresponding toGG‘ were observed in xenon matrices and the GG/GT intensity ratio became similar to the GG/(GT + GG‘)intensity ratio observed in argon matrices. All these results could be explained by taking into account therelative values of the theoretically predicted energy barriers for the different isomerization processes: GG‘→GT,1.90 kJ mol-1; GT→GG, 9.64 kJ mol-1; and GG‘→GG, 19.46 kJ mol-1.
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