Infrared absorption of CH3SO2 observed upon irradiation of a p-H-2 matrix containing CH3I and SO2

Abstract

Irradiation with a mercury lamp at 254 nm of a p-H-2 matrix containing CH3I and SO2 at 3.3 K, followed by annealing of the matrix, produced prominent features at 633.8, 917.5, 1071.1 (1072.2), 1272.5 (1273.0, 1273.6), and 1416.0 cm(-1), attributable to nu(11) (C-S stretching), nu(10) (CH3 wagging), nu(8) (SO2 symmetric stretching), nu(7) (SO2 antisymmetric stretching), and nu(4) (CH2 scissoring) modes of methylsulfonyl radical (CH3SO2), respectively; lines listed in parentheses are weaker lines likely associated with species in a different matrix environment. Further irradiation at 365 nm diminishes these features and produced SO2 and CH3. Additional features at 1150.1 and 1353.1 (1352.7) cm(-1) are tentatively assigned to the SO2 symmetric and antisymmetric stretching modes of ISO2. These assignments are based on comparison of observed vibrational wavenumbers and O-18- and S-34-isotopic shifts with those predicted with the B3P86 method. Our results agree with the previous report of transient IR absorption bands of gaseous CH3SO2 at 1280 and 1076 cm(-1). These results demonstrate that the cage effect of solid p-H-2 is diminished so that CH3 radicals, produced via UV photodissociation of CH3I in situ, might react with SO2 to form CH3SO2 during irradiation and upon annealing. Observation of CH3SO2 but not CH3OSO is consistent with the theoretical predictions that only the former reactions proceed via a barrierless path. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567117]