Photodissociation of thiophosgene

Abstract

The photolysis of thiophosgene produces CS(A 1π) below the incident wavelength (1270 Å) from which ΔHf °0(SCCl2) ?7.92±1 kcal mol−1 (33.1±4 kJ mol−1) is derived. The quantum yield for the production of Cl atoms has been determined from the amounts of HCl produced from the photolysis of thiophosgene–heptane mixtures. At 2537 Å the yield is unity over the pressure region 0.4–80 torr (0.05–10 kPa) of thiophosgene, indicating that the primary photochemical process is almost entirely SCCl+Cl. Both at 3660 and 4358 Å the quantum yield of Cl production increases with a decrease in thiophosgene pressure and is 0.90±0.17 and 0.38±0.19, respectively, as the pressure approaches zero. From the pressure dependence of the quantum yield the lifetime of the excited state 1A2 is estimated to be about 55 nsec at 4358 Å and about 6 nsec at 3660 Å. The photolysis data of the 1A2 state of thiophosgene are correlated with the fluorescence lifetime measured previously. D°0(SCCl–Cl) =63.4±0.5 kcal mol−1 (265.3±2 kJ mol−1) and ΔHf °0(SCCl) =43±1 kcal mol−1 (180±4 kJ mol−1) are derived. The photochemistry of thiophosgene is compared with that of phosgene and formaldehyde. A new method of Cl isotopic enrichment is suggested.