Four-centered concerted ethane elimination in the IR and UV laser photolysis of dimethyldisulfide. Real-time observation of S2 and CH3S radicals

Kumar, Awadhesh; Chowdhury, P.; Rao, K. V. S. Rama; Mittal, Jai P.

doi:10.1016/0009-2614(92)85073-j

Cited by 15 publications

(20 citation statements)

References 25 publications

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“…Based on these results, it is concluded that C 2 H 6 is eliminated from the cyclic transition state, during multiphoton excitation of neutral CH 3 SSCH 3 at 355 nm, and this C 2 H 6 is subsequently ionised to give C 2 H 6 + . This conclusion is consistent with the results of Kumar et al 9 who detected C 2 H 6 in the photolysed products using a gas chromatographic technique. It may be mentioned that the small signal corresponding to m/e 30 does not imply that the quantum yield for this channel is low.…”

Section: Discussionsupporting

confidence: 93%

“…It may be mentioned that the small signal corresponding to m/e 30 does not imply that the quantum yield for this channel is low. Kumar et al 9 measured a quantum yield of 0.4 at 248 nm for this channel. Since the ionisation potential of C 2 H 6 is 11.56 eV, it will require four photons for its ionisation at 355 nm as compared to other radicals, which need two/three photons.…”

Section: Discussionmentioning

confidence: 88%

“…In photolysis studies of CH 3 SSCH 3 at wavelengths between 230–280 nm, it was concluded that the primary process is direct production of two CH 3 S radicals 7,. 8 However, Kumar et al 9 claimed that two major dissociation channels, namely, CH 3 S + CH 3 S and S 2 + C 2 H 6 (channels (1) and (4)), operate when CH 3 SSCH 3 is photolysed at 248 nm. Transient UV spectra of CH 3 , CH 3 S, CH 2 S and S 2 radicals were observed in the flash photolysis of CH 3 SSCH 3 at 195 nm excitation 10.…”

mentioning

confidence: 99%

“…There has been some controversy regarding the formation of C 2 H 6 and S 2 during the photodissociation of DMDS at 248 nm. Kumar et al 9 measured a quantum yield of 0.4 for the C 2 H 6 + S 2 channel and suggested that C 2 H 6 is produced by simultaneous breaking of the two S‐C bonds of the CH 3 SSCH 3 in the four‐centred cyclic transition state. These authors did not suggest the occurrence of channel (2).…”

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confidence: 99%

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Multiphoton dissociation/ionisation of dimethyl sulfide

Vatsa

Majumder

Jayakumar

et al. 2001

Rapid Comm Mass Spectrometry

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Multiphoton dissociation/ionisation studies have been carried out at 355 nm for dimethyl disulfide (CH 3 SSCH 3 ) using a time-of-flight-mass spectrometer. The ultraviolet (UV) absorption spectra of DMDS show two bands with maxima at 250 and 195 nm. 5,6 The first band has been attributed to the promotion of a nonbonding electron from sulfur to an antibonding orbital localised in the S-S bond (n S → s* SÀS transition). The second band at 195 nm has been assigned to n S → s* SÀS as well as n S → s* CÀS transition. In photolysis studies of CH 3 SSCH 3 at wavelengths between 230±280 nm, it was concluded that the primary process is direct production of two CH 3 S radicals. 7,8However, Kumar et al. 9 claimed that two major dissociation channels, namely, CH 3 S CH 3 S and S 2 C 2 H 6 (channels (1) and (4) that about 80% of the CH 3 S 2 produced from the C-S bond cleavage contained sufficient internal energy to undergo a spontaneous dissociation into S 2 and CH 3 radicals. The quantum yield of CH 3 S was measured to be 1.65 AE 0.38 at 248 nm and 1.2 AE 0.14 at 193 nm during the photolysis of DMDS, thereby suggesting that, in addition to S-S cleavage, other channels also exist at both these wavelengths. 12 For excitation in the region 140±200 nm, it was shown that the photodissociation of CH 3 SSCH 3 produces predominantly CH 3 S(A Ä ) CH 3 S(X). 13Photoionisation of DMDS has also been studied 14,15 using TOFMS. Chiang et al. 14 showed the formation of only a parent ion when DMDS was excited by 117.4 nm (10.56 eV) using synchrotron radiation. At wavelengths below 110 nm (11.27 eV), a peak at m/e 45 (HCS ) was also observed which was suggested to originate from the dissociation of the excited parent ion. ) along with the parent ion were observed for this energy range.There has been some controversy regarding the formation of C 2 H 6 and S 2 during the photodissociation of DMDS at 248 nm. Kumar et al.9 measured a quantum yield of 0.4 for the C 2 H 6 S 2 channel and suggested that C 2 H 6 is produced by simultaneous breaking of the two S-C bonds of the CH 3 SSCH 3 in the four-centred cyclic transition state. These authors did not suggest the occurrence of channel (2). Suzuki et al. 16 detected S 2 in their laser-induced fluorescence experiments when CH 3 SSCH 3 was photolysed at 248 nm. However, the direct detection of dissociation products using a TOF mass spectrometer by Lee et al.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionmentioning

confidence: 88%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Multiphoton dissociation/ionisation of dimethyl sulfide

Vatsa

Majumder

Jayakumar

et al. 2001

Rapid Comm Mass Spectrometry

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“…Previous experiments using chemical analytic methods, 6 ion time-of-flight, 7 UV absorption spectroscopy, 8 and photoelectron detection 9 observed predominantly dissociation into two methyl-thiyl (CH 3 S) radicals after UV excitation between 230 and 266 nm. In contrast, resonance Raman spectroscopy 10 of gas-phase DMDS and a very recent picosecond sulfur Kedge TRXAS of DMDS in solution, 11 both using 266 nm excitation, indicated predominant scission of a C−S bond, although secondary reactions could play a role.…”

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confidence: 99%

Tracing the 267 nm-Induced Radical Formation in Dimethyl Disulfide Using Time-Resolved X-ray Absorption Spectroscopy

Schnorr

Bhattacherjee

Oosterbaan

et al. 2019

J. Phys. Chem. Lett.

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Disulfide bonds are pivotal for the structure, function, and stability of proteins, and understanding ultraviolet (UV)-induced S−S bond cleavage is highly relevant for elucidating the fundamental mechanisms underlying protein photochemistry. Here, the near-UV photodecomposition mechanisms in gas-phase dimethyl disulfide, a prototype system with a S−S bond, are probed by ultrafast transient X-ray absorption spectroscopy. The evolving electronic structure during and after the dissociation is simultaneously monitored at the sulfur L 1,2,3-edges and the carbon K-edge with 100 fs (FWHM) temporal resolution using the broadband soft X-ray spectrum from a femtosecond high-order harmonics light source. Dissociation products are identified with the help of ADC and RASPT2 electronic-structure calculations. Rapid dissociation into two CH 3 S radicals within 120 ± 30 fs is identified as the major relaxation pathway after excitation with 267 nm radiation. Additionally, a 30 ± 10% contribution from asymmetric CH 3 S 2 + CH 3 dissociation is indicated by the appearance of CH 3 radicals, which is, however, at least partly the result of multiphoton excitation.

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Kinetics investigation of the hydrogen abstraction reaction between CH3SS and CN radicals

et al. 2016

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The reaction mechanisms and rates for the H abstraction reactions between CH3SS and CN radicals in the gas phase were investigated with density functional theory (DFT) methods. The geometries, harmonic vibrational frequencies, and energies of all stationary points were obtained at B3PW91/6-311G(d,p) level of theory. Relationships between the reactants, intermediates, transition states and products were confirmed, with the frequency and the intrinsic reaction coordinate (IRC) analysis at the same theoretical level. High accurate energy information was provided by the G3(MP2) method combined with the standard statistical thermodynamics. Gibbs free energies at 298.15 K for all of the reaction steps were reported, and were used to describe the profile diagrams of the potential energy surface. The rate constants were evaluated with both the classical transition state theory and the canonical variational transition state theory, in which the small-curvature tunneling correction was included. A total number of 9 intermediates (IMs) and 17 transition states (TSs) were obtained. It is shown that IM1 is the most stable intermediate by the largest energy release, and the channel of CH3SS + CN → IM3 → TS10 → P1(CH2SS + HCN) is the dominant reaction with the lowest energy barrier of 144.7 kJ mol(-1). The fitted Arrhenius expressions of the calculated CVT/SCT rate constants for the rate-determining step of the favorable channel is k =7.73 × 10(6) T (1.40)exp(-14,423.8/T) s(-1) in the temperature range of 200-2000 K. The apparent activation energy E a(app.) for the main channel is -102.5 kJ mol(-1), which is comparable with the G3(MP2) energy barrier of -91.8 kJ mol(-1) of TS10 (relative to the reactants).

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Four-centered concerted ethane elimination in the IR and UV laser photolysis of dimethyldisulfide. Real-time observation of S2 and CH3S radicals

Cited by 15 publications

References 25 publications

Multiphoton dissociation/ionisation of dimethyl sulfide

Multiphoton dissociation/ionisation of dimethyl sulfide

Tracing the 267 nm-Induced Radical Formation in Dimethyl Disulfide Using Time-Resolved X-ray Absorption Spectroscopy

Kinetics investigation of the hydrogen abstraction reaction between CH3SS and CN radicals

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