15min:

YUAN-PERN LEE, Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan; JIN-DAH CHEN, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan .

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 reaction intermediates produced upon UV irradiation of a flowing mixture of CH₃SSCH₃ and NO₂ in CO₂. Irradiation of CH₃SSCH₃ at 248 nm produces CH₃S radicals that subsequently react with NO₂. Under a total pressure of 100 Torr, we observed bands near 1560 cm^-1, assignable to mainly the N=O stretching mode of CH₃SONO, with a small contribution from CH₃SNO₂. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational wavenumbers, and rotational parameters of CH₃SONO and CH₃SNO₂. Based on these predicted rotational parameters, the simulated absorption band agrees satisfactorily with experimental results. Under a total pressure of 16 Torr, bands near 1560 and 1260 cm^-1 are assigned to NO₂ asymmetric and symmetric stretching modes of CH₃SNO₂, respectively; the former is overlapped with the N=O stretching mode of CH₃SONO. An additional band near 1070 cm^-1 is assigned to the S=O stretching mode of CH₃SO, reported previously as a secondary product in the reaction of CH₃S + O₂. Reaction of CH₃S + NO₂ at high pressure clearly yields CH₃SONO, rather than CH₃SNO₂, as a major product.