The SO2(3B1) photosensitized isomerization of cis‐ and trans‐1,2‐dichloroethylene

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Abstract
The photolysis of SO2 at 3712 Å in the presence of the 1,2‐dichloroethylenes has been investigated at 22deg;C. The data are consistent with the SO2(3B1) photosensitized isomerization of the 1,2‐dichloroethylene isomer. A kinetic treatment of the initial quantum yield data was consistent with the formation of a polarized charge‐transfer intermediate whenever SO2(3B1) molecules and one of the 1,2‐dichloroethylene isomers collide which ultimately decays unimolecularly to the cis‐isomer with a probability of 0.70 ± 0.26 and to the trans‐isomer with a 0.37 ± 0.16 probability. Quenching rate constants for removal of SO2(3B1) molecules by cis‐ and trans‐1,2‐dichloroethylene have been estimated from quantum yield data and from laser excited phosphorescence lifetimes using an excitation wavelength of 3130 Å. Estimates of the quenching rate constant (units of 1./mole ± sec) are for the cis‐isomer, (1.63 ± 0.71) × 1010, quantum yield data, and (2.44 ± 0.11) × 1010, lifetime data; and for the trans‐isomer,(2.59 ± 0.09)×1010, lifetime data, and (2.35 ±0.89) × 1010, quantum yield data. An experimentally determined photostationary composition,[cis‐C2Cl2H2]/[trans‐C2Cl2H2] = 1.8 ‐ 0.1, was in good agreement with a value of 2.00 ‐ 1.15 which was predicted from rate constants derived in this study.