Abstract
A step-scan Fourier-transform spectrometer coupled with a 6.4 m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH 3 SO 2 radical, produced upon irradiation of a flowing gaseous mixture of CH 3 I and SO 2 in CO 2 at 248 nm. Two transient bands with origins at 1280 and 1076 cm -1 were observed and are assigned to the SO 2 -antisymmetric and SO 2 -symmetric stretching modes of CH 3 SO 2 , respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH 3 SO 2 and CH 3 OSO. Based on predicted rotational parameters, the simulated absorption band of the SO 2 -antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm -1 observed at a later period is tentatively attributed to CH 3 SO 2 I. The reaction kinetics of CH 3 + SO 2 →CH 3 SO 2 and CH 3 SO 2 +I→CH 3 SO 2 I based on the rise and decay of absorption bands of CH 3 SO 2 and CH 3 SO 2 I agree satisfactorily with previous reports. © 2006 American Institute of Physics.