Franck-Condon Dominated Chemistry. Formation and Dissociations of the Dimethylhydroxysulfuranyl Radical

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Title:Franck-Condon Dominated Chemistry. Formation and Dissociations of the Dimethylhydroxysulfuranyl Radical
Creators:
Tureček, František
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 65, 4, pp. 455-476
Uncontrolled Keywords:Mass spectrometry, <i>Ab initio</i> calculations, Atmospheric chemistry, Gas-phase chemistry, Radicals, Oxidations, Dimethyl sulfide, Dimethyl sulfoxide

Abstract

The structure and energetics of the hydroxyl radical adduct to dimethyl sulfide (DMS) was revisited using high level <i>ab initio</i> calculations. Density functional theory B3LYP/6-31++G(2d,p) and perturbational MP2(FULL)/6-31++G(2d,p) calculations found a weakly bound structure, (CH<sub>3</sub>)<sub>2</sub>SOH<sup>•</sup>, with a long S-O bond that was a local energy minimum. Single point calculations at the effective QCISD(T)/6-311++G(3df,2p) level of theory, denoted as G2++(MP2), found the (CH<sub>3</sub>)<sub>2</sub>S-OH<sup>•</sup> bonding energy to be 40 kJ mol<sup>-1</sup> at 298 K. The standard heat of formation of (CH<sub>3</sub>)<sub>2</sub>SOH<sup>•</sup> was assessed from dissociation and isodesmic reactions as -45 ± 4 kJ mol<sup>-1</sup>. No other local minima corresponding to C<sub>2</sub>H<sub>7</sub>OS radicals were found at the present level of theory that could be derived from DMS or dimethyl sulfoxide (DMSO). A very weak complex, CH<sub>3</sub>S(H)-<sup>•</sup>OCH<sub>3</sub>, was found that was bound by mere 4 kJ mol<sup>-1</sup> against dissociation to CH<sub>3</sub>SH and <sup>•</sup>OCH<sub>3</sub>. Vertical electron capture by (CH<sub>3</sub>)<sub>2</sub>SOH<sup>+</sup> is predicted to form (CH<sub>3</sub>)<sub>2</sub>SOH<sup>•</sup> with a highly non-relaxed geometry corresponding to a vibrational excitation of 138 kJ mol<sup>-1</sup> above the local minimum and 88 kJ mol<sup>-1</sup> above the dissociation threshold to DMS and OH<sup>•</sup>. Unimolecular dissociation of (CH<sub>3</sub>)<sub>2</sub>SOH<sup>•</sup> to methanesulfenic acid (CH<sub>3</sub>SOH) and <sup>•</sup>OCH<sub>3</sub> faces an energy barrier that diminishes at shorter S-O distances. The dipole-allowed electronic excitation in (CH<sub>3</sub>)<sub>2</sub>SOH<sup>•</sup> was calculated with CIS/6-311++G(2df,p) to have λ<sub>max</sub> = 248 nm in the gas phase. The resulting <i>B</i> state represents a charge-transfer complex of (CH<sub>3</sub>)<sub>2</sub>S<sup>+•</sup> and OH<sup>-</sup>. The present computational results allowed us to explain the existing controversy between the experimental results obtained by gas-phase flow kinetics, radiolysis in aqueous solution, and neutralization-reionization mass spectrometry. <p>

Title:Franck-Condon Dominated Chemistry. Formation and Dissociations of the Dimethylhydroxysulfuranyl Radical
Creators:
Tureček, František
Uncontrolled Keywords:Mass spectrometry, <i>Ab initio</i> calculations, Atmospheric chemistry, Gas-phase chemistry, Radicals, Oxidations, Dimethyl sulfide, Dimethyl sulfoxide
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:65
Number:4
Page Range:pp. 455-476
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20000455UNSPECIFIED
ID Code:1654
Item Type:Article
Deposited On:06 Feb 2009 17:11
Last Modified:06 Feb 2009 16:11

Citation

Tureček, František (2000) Franck-Condon Dominated Chemistry. Formation and Dissociations of the Dimethylhydroxysulfuranyl Radical. Collection of Czechoslovak Chemical Communications, 65 (4). pp. 455-476. ISSN 0010-0765

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