Accurate thermochemistry and spectroscopy of the oxygen-protonated sulfur dioxide isomers.

Despite the promising relevance of protonated sulfur dioxide in astrophysical and atmospheric fields, its thermochemical and spectroscopic characterization is very limited. High-level quantum-chemical calculations have shown that the most stable isomer is the cis oxygen-protonated sulfur dioxide, HOSO(+), while the trans form is about 2 kcal mol(-1) less stable; even less stable (by about 42 kcal mol(-1)) is the S-protonated isomer [V. Lattanzi et al., J. Chem. Phys., 2010, 133, 194305]. The enthalpy of formation for the cis- and trans-HOSO(+) is presented, based on the well tested HEAT protocol [A. Tajti et al., J. Chem. Phys., 2004, 121, 11599]. Systematically extrapolated ab initio energies, accounting for electron correlation through coupled cluster theory, including up to single, double, triple and quadruple excitations, have been corrected for core-electron correlation, anharmonic zero-point vibrational energy, diagonal Born-Oppenheimer and scalar relativistic effects. As a byproduct, proton affinity of sulfur dioxide and atomization energies have also been obtained at the same levels of theory. Vibrational and rotational spectroscopic properties have been investigated by means of composite schemes that allow us to account for truncation of basis set as well as core correlation. Where available, for both thermochemistry and spectroscopy, very good agreement with experimental data has been observed.