Detection of transient infrared absorption of SO and 1,3,2-dioxathietane-2,2-dioxide [cyc-(CH)O(SO)O] in the reaction CHOO+SO.

We recorded time-resolved infrared absorption spectra of transient species produced on irradiation at 308 nm of a flowing mixture of CHI/O/N/SO at 298 K. Bands of CHOO were observed initially upon irradiation; their decrease in intensity was accompanied by the appearance of an intense band at 1391.5 cm that is associated with the degenerate SO-stretching mode of SO, two major bands of HCHO at 1502 and 1745 cm, and five new bands near >1340, 1225, 1100, 940, and 880 cm. The band near 1340 cm was interfered by absorption of SO and SO, so its band maximum might be greater than 1340 cm. SO in its internally excited states was produced initially and became thermalized at a later period. The rotational contour of the band of thermalized SO agrees satisfactorily with the reported spectrum of SO. These five new bands are tentatively assigned to an intermediate 1,3,2-dioxathietane-2,2-dioxide [cyc-(CH)O(SO)O] according to comparison with anharmonic vibrational wavenumbers and relative IR intensities predicted for this intermediate. Observation of a small amount of cyc-(CH)O(SO)O is consistent with the expected reaction according to the potential energy scheme predicted previously. SO+HCHO are the major products of the title reaction. The other predicted product channel HCOOH+SO was unobserved and its branching ratio was estimated to be <5%.