Transient infrared spectra of CH₃ SOO and CH₃ so observed with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to monitor time-resolved infrared absorption of transient species produced upon irradiation at 248 nm of a flowing mixture of CH₃ SSCH₃ and O₂ at 260 K. Two transient bands observed with origins at 1397±1 and 1110±3 cm-1 are tentatively assigned to the antisymmetric CH₃ -deformation and OO stretching modes of syn -CH₃ SOO, respectively; the observed band contour indicates that the less stable anti -CH₃ SOO conformer likely contributes to these absorption bands. A band with an origin at 1071±1 cm-1, observed at a slightly later period, is assigned to the SO stretching mode of CH₃ SO, likely produced via secondary reactions of CH₃ SOO. These bands fit satisfactorily with vibrational wavenumbers and rotational contours simulated based on rotational parameters of syn -CH₃ SOO, anti -CH₃ SOO, and CH₃ SO predicted with density-functional theories B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ. Two additional bands near 1170 and 1120 cm-1 observed at a later period are tentatively assigned to CH₃ S (O) OSCH₃ and CH₃ S (O) S (O) CH₃, respectively; both species are likely produced from self-reaction of CH₃ SOO. The production of SO₂ via secondary reactions was also observed and possible reaction mechanism is discussed.