Knowledge Bank

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$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ radical, produced upon irradiation of a flowing mixture of CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$I and SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ in CO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ at 248 nm. Two transient bands with origins at 1280 and 1076 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ were observed and assigned to the SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$-antisymmetric and SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$-symmetric stretching modes of CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational wave numbers, and rotational parameters of CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ and CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$OSO. Based on predicted rotational parameters, the simulated absorption band of SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$-antisymmetric stretch which is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ was observed at a later period and was attributed to CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$I. The reaction kinetics of CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ + SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ = CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ and CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ + I = CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$I based on the rise and decay of absorption bands of CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ and CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$SO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$I agree satisfactorily with previous reports.