Enthalpy of Formation of CH3SO and CH3SO2: A Difficult Case in Quantum Chemistry

Resende, Stella M.; Ornellas, Fernando R.

doi:10.1590/s0103-50532002000500004

Cited by 16 publications

(9 citation statements)

References 10 publications

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“…4(a). Absorption lines of the CH 3 I · 16 OS 16 Upon annealing, lines in groups A (CH 3 SO 2 ) and B (ISO 2 ) increased further in intensity, as shown in Fig. 2(c), but with different proportions.…”

Section: B Photolysis Of Ch 3 I/so 2 /P-h 2 Matricesmentioning

confidence: 83%

“…11 Several theoretical computations predict the energy, geometry, and vibrational wavenumbers of CH 3 SO 2 and methoxysulfinyl radical (CH 3 OSO). [12][13][14][15][16][17][18] According to the most extensive computations, reactions of CH 3 with SO 2 might proceed via two paths: a barrierless channel to produce CH 3 SO 2 and a channel with a barrier of 49-58 kJ mol −1 to produce two conformers of CH 3 OSO, syn-CH 3 OSO, and anti-CH 3 OSO; anti-CH 3 OSO might transform via a barrier of ∼1 kJ mol −1 to syn-CH 3 OSO that is more stable than anti-CH 3 OSO by ∼8 kJ mol −1 , and more stable than CH 3 SO 2 by 21−37 kJ mol −1 . [16][17][18] Isomerization from CH 3 SO 2 to syn-CH 3 OSO is unlikely because of a large barrier of ∼200 kJ mol −1 .…”

Section: Introductionmentioning

confidence: 99%

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Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Lee

2011

The Journal of Chemical Physics

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Irradiation with a mercury lamp at 254 nm of a p-H(2) matrix containing CH(3)I and SO(2) at 3.3 K, followed by annealing of the matrix, produced prominent features at 633.8, 917.5, 1071.1 (1072.2), 1272.5 (1273.0, 1273.6), and 1416.0 cm(-1), attributable to ν(11) (C-S stretching), ν(10) (CH(3) wagging), ν(8) (SO(2) symmetric stretching), ν(7) (SO(2) antisymmetric stretching), and ν(4) (CH(2) scissoring) modes of methylsulfonyl radical (CH(3)SO(2)), respectively; lines listed in parentheses are weaker lines likely associated with species in a different matrix environment. Further irradiation at 365 nm diminishes these features and produced SO(2) and CH(3). Additional features at 1150.1 and 1353.1 (1352.7) cm(-1) are tentatively assigned to the SO(2) symmetric and antisymmetric stretching modes of ISO(2). These assignments are based on comparison of observed vibrational wavenumbers and (18)O- and (34)S-isotopic shifts with those predicted with the B3P86 method. Our results agree with the previous report of transient IR absorption bands of gaseous CH(3)SO(2) at 1280 and 1076 cm(-1). These results demonstrate that the cage effect of solid p-H(2) is diminished so that CH(3) radicals, produced via UV photodissociation of CH(3)I in situ, might react with SO(2) to form CH(3)SO(2) during irradiation and upon annealing. Observation of CH(3)SO(2) but not CH(3)OSO is consistent with the theoretical predictions that only the former reactions proceed via a barrierless path.

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Section: B Photolysis Of Ch 3 I/so 2 /P-h 2 Matricesmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Lee

2011

The Journal of Chemical Physics

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“…The DH f o for CH 3 SO 2 is the one obtained in a previous high level theoretical study, -218.4 kJ mol -1 . 28,29 The values for the calculated reaction enthalpies are collected in the first column of Table 2. The average value obtained for MSA is -566.2 kJ mol -1 .…”

Section: Resultsmentioning

confidence: 99%

Theoretical determination of the properties of Methanesulfinic and Methanesulfonic acids

Carvalho¹,

Silva²,

Resende³

2011

J. Braz. Chem. Soc.

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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 ...

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“…[43][44][45] The MG3S basis set fulfils this requirement. It is a basis set 46 identical to 6-3111G(2df) for C and O and to 311G(2p) for H. For the sulfur atom, this basis set stands for the 6-3111G(3d2f) Pople's one.…”

Section: Computational Detailsmentioning

confidence: 99%

Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O₂

2011

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The chemical tropospheric dimethyl sulfide (DMS, CH3SCH3) degradation involves several steps highly dependent on the environmental conditions. So, intensive efforts have been devoted during the last years to enhance the understanding of the DMS oxidation mechanism under different conditions. The reaction of DMS with OH is considered to be the most relevant process that initiates the whole oxidation process. The experimental observations have been explained by a two-channel mechanism consisting of a H-abstraction process leading to CH3S(O)CH3 and HO2 and an addition reaction leading to the DMS·OH adduct. In the presence of O2, the DMS·OH adduct is competitively scavenged increasing the contribution of the addition channel to the overall DMS oxidation. Recent experimental measurements have determined from a global fit that the rate constant of this scavenging process is independent of pressure and temperature but this rate constant cannot be directly measured. In this article, a variational transition-state theory calculation of the low- and high-pressure rate constants for the reaction between DMS·OH and O2 has been carried out as a function of temperature. Our proposal is that the slight temperature dependence of the scavenging rate constant can only be explained if the H-abstraction bottleneck is preceded by a dynamical bottleneck corresponding to the association process between the DMS·OH adduct and the O2 molecule. The agreement between the low-pressure and high-pressure rate constants confirms the experimental observations.

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Enthalpy of Formation of CH3SO and CH3SO2: A Difficult Case in Quantum Chemistry

Cited by 16 publications

References 10 publications

Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Theoretical determination of the properties of Methanesulfinic and Methanesulfonic acids

Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O₂

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Enthalpy of Formation of CH3SO and CH3SO2: A Difficult Case in Quantum Chemistry

Cited by 16 publications

References 10 publications

Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Infrared absorption of CH3SO2 observed upon irradiation of a p-H2 matrix containing CH3I and SO2

Theoretical determination of the properties of Methanesulfinic and Methanesulfonic acids

Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O2

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Product

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Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O₂