As propriedades estruturais, espectroscópicas e termodinâmicas de duas espécies de enxofre de interesse atmosférico, ácidos metanosulfínico (CH 3 S(O)OH, MSIA) e metanosulfônico (CH 3 S(O) 2 OH, MSA) foram determinadas no nível de CCSD(T)/CBS (coupled-cluster with single and double and perturbative triple excitations/complete basis set) de teoria. Duas conformações foram encontradas para o ácido metanosulfínico e o valor médio determinado para a entalpia de formação foi -337,2 kJ mol -1 . Para o ácido metanosulfônico, o resultado para a entalpia de formação foi 566,2 kJ mol -1 . Escolhendo cuidadosamente as reações químicas e considerando a existência de duas conformações de MSIA, esta investigação reporta os valores mais precisos de DH f disponíveis até agora para estas espécies.The structural, spectroscopic and thermochemical properties of two sulfur species of atmospheric interest, methanesulfinic (CH 3 S(O)OH, MSIA) and methanesulfonic (CH 3 S(O) 2 OH, MSA) acids, were determined at the CCSD(T)/CBS (coupled-cluster with single and double and perturbative triple excitations/complete basis set) level of theory. Two stable conformers were found to the methanesulfinic acid, and the determined average value for the enthalpy of formation (DH f ) was -337.2 kJ mol -1 . For methanesulfonic acid, the determined enthalpy of formation was 566.2 kJ mol -1 . By carefully choosing of the chemical reactions and considering the existence of two MSIA conformers, this investigation reports the most accurate DH f values available to date for these species.
Keywords: dimethyl sulfide, enthalpy of formation, CCSD(T)/CBS theory
IntroductionDimethyl sulfide (DMS), generated in the ocean by phytoplankton, is an important natural source of sulfur in the atmosphere. 1 The main final products of its atmospheric decomposition are sulfuric acid and sulfate ions, which are key species in the climate regulation, due to the fact that they are precursors of aerosols. Sulfur aerosols act in the global warming producing a negative radiative forcing, dispersing the solar radiation and increasing the albedo. 2 Besides, due to the low gas pressure and polarity, these species can act as cloud condensation nuclei (CCN), condensing water molecules. 3,4 Several experimental and theoretical investigations of the oxidation of DMS in gas phase were conducted 5-7 and studies for OH-initiated reaction had revealed methanesulfonic acid (CH 3 S(O) 2 OH, MSA) 8 and methanesulfinic acid (CH 3 S(O) OH, MSIA) 9 as two key intermediates. In general, there are some difficulties in the characterization of the products, and the values of product yields reported can differ significantly. It is generally accepted that MSA is produced from the OH addition to DMS, in a mechanism highly dependent on temperature and O 2 partial pressure. On the other hand, the presence of MSIA in the atmospheric decomposition of DMS was proposed by Yin et al., 10 as a second-generation product of the DMS oxidation. However, the mechanism and the yields of MSIA formation were reasons of ...
