Infrared absorption of CH₃OSO detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to detect temporally resolved infrared absorption spectra of CH₃OSO produced upon irradiation of a flowing gaseous mixture of CH₃OS(O)Cl in N₂ or CO₂ at 248 nm. Two intense transient features with origins near 1152 and 994 cm^-1 are assigned to syn-CH₃OSO; the former is attributed to overlapping bands at 1154 ± 3 and 1151 ± 3 cm^-1, assigned to the SO stretching mixed with CH₃ rocking (₈) and the SO stretching mixed with CH₃ wagging (₉) modes, respectively, and the latter to the C-O stretching (₁₀) mode at 994 ± 6 cm^-1. Two weak bands at 2991 ± 6 and 2956 ± 3 cm ^-1 are assigned as the CH₃ antisymmetric stretching ( ₂) and symmetric stretching (₃) modes, respectively. Observed vibrational transition wavenumbers agree satisfactorily with those predicted with quantum-chemical calculations at level B3P86aug-cc-pVTZ. Based on rotational parameters predicted at that level, the simulated rotational contours of these bands agree satisfactorily with experimental results. The simulation indicates that the SO stretching mode of anti-CH₃OSO near 1164 cm^-1 likely makes a small contribution to the observed band near 1152 cm^-1. A simple kinetic model of self-reaction is employed to account for the decay of CH₃OSO and yields a second-order rate coefficient k (4 ± 2)10^-10 cm³ molecule ^-1 s^-1.