Photochemistry of Low-Temperature Matrices Containing Carbonyl Sulfide: Reactions of Sulfur Atoms with the Phosphorus Trihalides PF3 and PCl3 and the Hydrocarbons CH4, C2H4, and C2H2

Article abstract of DOI:10.1021/j100261a034

Exposure of a solid argon matrix containing the molecules OCS and PX3 (X = F or Cl) at ca. 20 K to broad-band ultraviolet radiation leads to the formation of CO and the corresponding thiophosphorus(V) halides SPX3, as witnessed by the infrared spectrum of the matrix.Photolysis of a solid methane matrix containing OCS at 13-20 K on exposure to radiation with wavelengths near 230 nm gives rise to CO, methanethiol, CH3SH, thioformaldehyde, H2C=S, and carbon disulfide, CS2, as the only products to be detected by their infrared spectra.Yet there is no sign of either CH3SH or H2C=S on photolysis of OCS in a CH4-doped argon matrix with the composition Ar:CH4:OCS = 100:20:1.Evidently the photolysis of OCS generates ¹D sulfur atoms which add to an adjacent CH4 molecule with the formation of a vibrationally activated intermediate ^*; this relaxes to give CH3SH or decomposes to give H2C=S.Similar experiments have been carried out with solid argon matrices including OCS and either C2H4 or C2H2.In the presence of C2H4 there is no hint of C-H insertion; instead the C2H4 undergoes sulfur atom addition at the double bond to give thiirane, , as the sole product to be identified by its infrared spectrum.By contrast, C2H2 yields thioketene, H2C=S, ethynethiol, HCCSH, and carbon disulfide, CS2, as the main products, as well as thiirane, , as a minor product.The response of the hydrocarbon molecules in argon matrices can be interpreted in terms of the diffusion and reaction of ground-state ³P sulfur atoms but not of ¹D sulfur atoms which are too short-lived to undergo significant migration.It appears that ³P sulfur atoms react with both C2H4 and C2H2 to yield a triplet diradical: that derived from C2H4 favors cyclization, whereas that derived from C2H2 rearranges preferentially to H2C=C=S and this in turn enters into secondary reactions to give HCCSH and CS2.