The dissociation of vibrationally excited CH3OSO radicals and their photolytic precursor, methoxysulfinyl chloride

Abstract

The dissociation dynamics of methoxysulfinyl radicals generated from the photodissociation of CH(3)OS(O)Cl at 248 nm is investigated using both a crossed laser-molecular beam scattering apparatus and a velocity map imaging apparatus. There is evidence of only a single photodissociation channel of the precursor: S-Cl fission to produce Cl atoms and CH(3)OSO radicals. Some of the vibrationally excited CH(3)OSO radicals undergo subsequent dissociation to CH(3) + SO(2). The velocities of the detected CH(3) and SO(2) products show that the dissociation occurs via a transition state having a substantial barrier beyond the endoergicity; appropriately, the distribution of velocities imparted to these momentum-matched products is fit by a broad recoil kinetic energy distribution extending out to 24 kcal/mol in translational energy. Using 200 eV electron bombardment detection, we also detect the CH(3)OSO radicals that have too little internal energy to dissociate. These radicals are observed both at the parent CH(3)OSO(+) ion as well as at the CH(3)(+) and SO(2)(+) daughter ions; they are distinguished by virtue of the velocity imparted in the original photolytic step. The detected velocities of the stable radicals are roughly consistent with the calculated barriers (both at the CCSD(T) and G3B3 levels of theory) for the dissociation of CH(3)OSO to CH(3) + SO(2) when we account for the partitioning of internal energy between rotation and vibration as the CH(3)OSOCl precursor dissociates.

Infrared absorption of CH3OSO and CD3OSO radicals produced upon photolysis of CH3OS(O)Cl and CD3OS(O)Cl in p-H2 matrices

“…The observed lines in group A do not match those reported for CH 3 SO 2 in solid p-H 2 at 1416.0, 1272.5, 1071.1, 917.5, and 633.8 cm −1 , 27 nor do they match those of ClSO 2 in solid Ar or those predicted for ClOSO. 44 Although two intense lines of CH 3 OS(O)O, the product reported after photolysis of (CH 3 O) 2 SO at 248 nm, 49 are predicted to have anharmonic vibrational wavenumbers (986 and 680 cm −1 ) similar to those observed in group A (989.7 and 714.5 cm −1 ), two additional intense lines predicted at 1261 and 1078 cm −1 were unobserved in our experiments.…”

“…According to Alligood et al, only the S−Cl fission channel to produce Cl atom and CH 3 OSO radical was observed upon photolysis of CH 3 OS(O)Cl at 248 nm. 49 Some vibrationally excited CH 3 OSO radicals undergo subsequent dissociation to CH 3 + SO 2 . The dissociation threshold to form CH 3 OSO + Cl is calculated to be 239 kJ mol −1 , corresponding to a wavelength of 501 nm.…”

“…The dissociation threshold to form CH 3 OSO + Cl is calculated to be 239 kJ mol −1 , corresponding to a wavelength of 501 nm. 49 With a filter to pass either 239 ± 20 nm or 254 ± 10 nm, we employed emission from a Hg lamp with the expectation that the light dissociates CH 3 OS(O)Cl and that the major products are CH 3 OSO and Cl.…”

“…The photolysis of (CH 3 O) 2 SO at 248 nm was investigated by Alligood et al who reported the main photodissociation products to be CH 3 and CH 3 OS(O)O. 49 Although SO 2 has an absorption cross section ∼2 × 10 −19 cm 2 molecule −1 at 254 nm (Ref. 50) and ∼3 × 10 −19 cm 2 molecule −1 at 226 nm, 51 its dissociation threshold of 543 kJ mol −1 to form SO + O corresponds to a wavelength of ∼220 nm.…”

Dissociative photoionization of CH3C(O)CH2 to C2H5+

“…Our data revealed that there were two major primary channels, C-Cl fission producing Cl and CH 3 C(O)CH 2 , as well as C-C fission to produce CH 3 CO and CH 2 Cl. We have since taken data to characterize a third photodissociation channel, one that yields CH 3 and COCH 2 Cl [7]. We used the crossed laser-molecular beam scattering apparatus to measure the distribution of velocities imparted to the Cl atoms upon C-Cl bond fission; the momentum-matched CH 3 C(O)CH 2 radicals were formed under collision-free conditions, which facilitated characterization of their internal energy distribution and subsequent dynamics.…”