High-Accuracy Theoretical Thermochemistry of Atmospherically Important Sulfur-Containing Molecules
journal contributionposted on 07.07.2011, 00:00 by Balázs Nagy, Péter Szakács, József Csontos, Zoltán Rolik, Gyula Tasi, Mihály Kállay
In this study, several sulfur-containing molecules with atmospherical importance were investigated by means of high-accuracy quantum chemical calculations including: HSO, HOS, HOSO2, HSNO, SH, CH2SO, CH2SH, S2COH, and SCSOH. After identifying the stable conformers of the molecules, a coupled-cluster-based composite model chemistry, which includes contributions up to quadruple excitations as well as corrections beyond the nonrelativistic and Born–Oppenheimer approximations, was applied to calculate the corresponding heat of formation (ΔfH0° and ΔfH298°) and entropy (S298°) values. In most of the cases, this study delivers more reliable estimates for the investigated thermodynamic properties than those reported in previous investigations. Our data also suggest that the experimental heats of formation associated with the HSO molecule are very likely to belong to its structural isomer, HOS. It is also confirmed by the calculated thermodynamic properties including standard reaction entropies, enthalpies, and equilibrium constants that, in the reaction CS2 + OH ⇄ CS2OH, the SCSOH structural isomer is produced. It is also noted that the currently accepted ΔfH0°(Sgas) = 274.73 ± 0.3 kJ/mol value is in need of revision, and based on a recent measurement, which is also confirmed by our computations, it is advised to update it to ΔfH0°(Sgas) = 277.25 ± 0.3 kJ/mol.