Dissociation dynamics of the methylsulfonyl radical and its photolytic precursor CH3SO2Cl

Abstract

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.

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

“…The 18 O-substitution experiment provides additional support for these assignments. As shown in Fig.…”

“…40) densityfunctional theories (DFT) with the aug-cc-pVTZ basis set. 41 In this work, we extended the calculations to obtain vibrational wavenumbers of 18 O-and 34 S-substituted CH 3 SO 2 and CH 3 OSO with the GAUSSIAN 09 program. 38 Vibrational wavenumbers and IR intensities for 34 S-and 18 O-isotopic species of CH 3 SO 2 predicted with the B3P86/aug-cc-pVTZ method are listed in Table I.…”

“…We performed an 18 Figure 3(a) indicates the regions in which lines in group A absorb; the spectrum was recorded from a sample of CH 3 I/ S 16 O 2 /p-H 2 (2.4/1.0/18900) upon irradiation at 254 nm, followed by annealing of the irradiated matrix at 4.9 K for 5 min. Figure 3(b) indicates the corresponding spectra recorded from the sample with CH 3 I/ 16 Figure 4(b) shows the corresponding difference spectrum recorded for the matrix sample CH 3 I/ 16 Vibrational wavenumbers of these observed lines in groups A and B and the CH 3 I · SO 2 complex for isotopic variants are summarized in Table III and compared with those derived based on theoretical calculations.…”

“…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 .…”

“…23 An UV absorption band with intensity maximum in the range 327-350 nm was ascribed to CH 3 SO 2 , produced in modulated UV photolysis of isooctane solutions containing sulfonyl chloride, triethylsilane, and ditert-butyl peroxide. 24,25 In the gaseous phase, both CH 3 SO 2 and CH 3 OSO were detected with a mass spectrometer 18 or a variabletime neutralization-reionization mass spectrometer; 12 in the latter system CH 3 SO 2 + was produced by dissociative ionization of dimethyl sulfone, (CH 3 ) 2 SO 2 , at 70 eV. Only two absorption bands of gaseous CH 3 SO 2 near 1280 and 1076 cm −1 were observed with a step-scan Fourier-transform infrared (FTIR) spectrometer when a flowing mixture of CH 3 I and SO 2 was irradiated at 248 nm; these two bands are assigned to the SO 2 antisymmetric and symmetric stretching modes of CH 3 SO 2 , respectively.…”