Methylsulfonyl Radical Unimolecular Dissociation Studied by Deep-UV Ultrafast Photoionization Spectroscopy

Owrutsky, Jeffrey C.; Nelson, H. H.; Baronavski, A. P.

doi:10.1021/jp001985+

Cited by 4 publications

(4 citation statements)

References 18 publications

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“…Using femtosecond mass-resolved photoionization spectroscopy, Owrutsky et al 16 measured a dissociation lifetime of 0.34 ps for CH 3 SO 2 radicals produced from the 196 nm photodissociation of CH 3 SO 2 Cl. They observed that fewer than 2% of the nascent CH 3 SO 2 radicals remain after 2 ps.…”

Section: Introductionmentioning

confidence: 99%

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Ratliff

Tang

Butler

et al. 2009

The Journal of Chemical Physics

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These imaging experiments study the formation of the methylsulfonyl radical, CH(3)SO(2), from the photodissociation of CH(3)SO(2)Cl at 193 nm and determine the energetic barrier for the radical's subsequent dissociation to CH(3) + SO(2). We first state-selectively detect the angular and recoil velocity distributions of the Cl((2)P(3/2)) and Cl((2)P(1/2)) atoms to further refine the distribution of internal energy partitioned to the momentum-matched CH(3)SO(2) radicals. The internal energy distribution of the radicals is bimodal, indicating that CH(3)SO(2) is formed in both the ground state and low-lying excited electronic states. All electronically excited CH(3)SO(2) radicals dissociate, while those formed in the ground electronic state have an internal energy distribution which spans the dissociation barrier to CH(3) + SO(2). We detect the recoil velocities of the energetically stable methylsulfonyl radicals with 118 nm photoionization. Comparison of the total recoil translational energy distribution for all radicals to the distribution obtained from the detection of stable radicals yields an onset for dissociation at a translational energy of 70+/-2 kcal/mol. This onset allows us to derive a CH(3)SO(2) --> CH(3) + SO(2) barrier height of 14+/-2 kcal/mol; this determination relies on the S-Cl bond dissociation energy, taken here as the CCSD(T) predicted energy of 65.6 kcal/mol. With 118 nm photoionization, we also detect the velocity distribution of the CH(3) radicals produced in this experiment. Using the velocity distributions of the SO(2) products from the dissociation of CH(3)SO(2) to CH(3) + SO(2) presented in the following paper, we show that our fastest detected methyl radicals are not from these radical dissociation channels, but rather from a primary S-CH(3) bond photofission channel in CH(3)SO(2)Cl. We also present critical points on the ground state potential energy surface of CH(3)SO(2) at the //CCSD(T)/aug-cc-pV(Q + d)ZCCSD(T)/6-311++G(2df,p) level. We include harmonic zero-point vibrational corrections as well as core-valence and scalar-relativistic corrections. The CCSD(T) predicted barrier of 14.6 kcal/mol for CH(3)SO(2) --> CH(3) + SO(2) agrees well with our experimental measurement. These results allow us to predict the unimolecular dissociation kinetics of CH(3)SO(2) radicals and critique the analysis of prior time-resolved photoionization studies on this system.

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Section: Introductionmentioning

confidence: 99%

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Ratliff

Tang

Butler

et al. 2009

The Journal of Chemical Physics

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“…Previously published theoretical work pertaining to the CH 3 SO 2 system highlights the need for concrete experimental data regarding the energetics along the dominant reaction channels. [4][5][6] Table I gives the barrier heights for the dissociation of CH 3 SO 2 to CH 3 +SO 2 , as calculated at various levels of theory. Zhu and Bozzelli 5 compared their computational results and concluded that, while G3 methods gave good energetics, the CCSD͑T͒ method was unreliable.…”

Section: Introductionmentioning

confidence: 99%

Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl

Alligood

FitzPatrick

Glassman

et al. 2009

The Journal of Chemical Physics

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The dissociation dynamics of methylsulfonyl radicals generated from the photodissociation of CH(3)SO(2)Cl at 193 nm is investigated by measuring product velocities in a crossed laser-molecular beam scattering apparatus. The data evidence three primary photodissociation channels of the precursor: S-Cl fission to produce Cl atoms and ground electronic state CH(3)SO(2) radicals, S-Cl fission to produce Cl atoms and electronically excited CH(3)SO(2) radicals, and S-CH(3) fission. Some of the vibrationally excited CH(3)SO(2) radicals undergo subsequent dissociation to CH(3) + SO(2), as do all of the electronically excited radicals. The velocities of the SO(2) products show that the vibrationally excited ground state CH(3)SO(2) radicals dissociate via a loose transition state having a small exit barrier beyond the endoergicity. Hence, a statistical recoil kinetic energy distribution should and does fit the distribution of velocities imparted to these SO(2) products. The electronically excited CH(3)SO(2) radicals also dissociate to CH(3) + SO(2), but with a larger average release to relative kinetic energy. Interestingly, when using 200 eV electron bombardment detection, the ground electronic state CH(3)SO(2) radicals having too little internal energy to dissociate are not observed at the parent CH(3)SO(2)(+) ion, but only at the CH(3)(+) daughter ion. They are distinguished by virtue of the velocity imparted in the original photolytic step; the detected velocities of the stable radicals are consistent with the calculated barrier of 14.6 kcal/mol for the dissociation of CH(3)SO(2) to CH(3) + SO(2). We present CCSD(T) calculations of the adiabatic excitation energy to the lowest excited state of CH(3)SO(2) radicals, the 1 (2)A(") state, as well as the vertical energy from the equilibrium geometry of that excited state to the 2 (2)A(") state, to aid in the experimental assignment.

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“…Sulfur‐containing radicals in tropospheric chemistry play an important role in the degradation mechanism of dimethyl sulfide (DMS). The methylsulfonyl radical, CH 3 S(O) 2 , is one of the most interesting and most extensively studied species in this mechanism. It is the more stable isomeric form of the weakly bound methylthiyl peroxyl radical, CH 3 SOO, readily formed in the atmosphere through the coupling of the methylthiyl radical, CH 3 S, with O 2

{CH}_{3} {S + O}_{2} \to {CH}_{3} SOO

{CH}_{3} SOO \to {CH}_{3} S (normalO)_{2} via isomerization

…”

Section: Introductionmentioning

confidence: 99%

“…Due to its significance in the oxidation mechanism of DMS, the dissociation and photoexcitation dynamics of CH 3 S(O) 2 radical have also been given considerable attention and its reactions with various atmospheric gases O 2 , O 3 , and NO x , have been examined in detail

{CH}_{3} S {(normalO)}_{2} {+ NO}_{2} \to products

…”

Section: Introductionmentioning

confidence: 99%

Computational study of the reaction of the methylsulfonyl radical, CH₃ S(O)₂ , with NO₂

Salta

Kosmas

2014

Int. J. Quantum Chem.

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The mechanism of the reaction between the methylsulfonyl radical, CH3S(O)2, and NO2 is examined using density functional theory and ab initio calculations. Two stable association intermediates, CH3SNO2 and CH3S(O)ONO, may be formed through the attack of the nitrogen or the oxygen atom of NO2 radical to the S atom. Interisomerization and decomposition of these intermediates are investigated using high level energy methods and specifically, CCSD(T), CBS‐QB3, and G3//B3LYP. The computational investigation indicates that the lowest energy reaction pathway leads to the products CH3S(O)3 + NO, through the decomposition of the most stable association adduct CH3S(O)ONO. This result fully supports the relevant assumption of Ray et al. (Ray et al., J. Phys. Chem. 1996, 100, 8895], on which the experimental evaluation of the rate constant was based, namely that CH3S(O)3 + NO are the most probable products of the reaction CH3S(O)2 + NO2. © 2014 Wiley Periodicals, Inc.

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Methylsulfonyl Radical Unimolecular Dissociation Studied by Deep-UV Ultrafast Photoionization Spectroscopy

Cited by 4 publications

References 18 publications

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl

Computational study of the reaction of the methylsulfonyl radical, CH₃ S(O)₂ , with NO₂

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Methylsulfonyl Radical Unimolecular Dissociation Studied by Deep-UV Ultrafast Photoionization Spectroscopy

Cited by 4 publications

References 18 publications

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Determining the CH3SO2→CH3+SO2 barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl

Computational study of the reaction of the methylsulfonyl radical, CH3 S(O)2 , with NO2

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Computational study of the reaction of the methylsulfonyl radical, CH₃ S(O)₂ , with NO₂