Photodissociation of RNCS and RSCN (R = H, CH₃, C ₂H₅) at 248 and 193 nm: CN product energy distributions

Photodissociation of the molecules RNCS and RSCN (R = H, CH₃, and C₂H₅) was investigated at 248 and 193 nm and the internal energy distributions in the CN resulting from the RS + CN fragmentation channel were probed by laser induced fluorescence. These CN distributions were identical for formation from the isomer pairs in agreement with an excited state isomerization postulated earlier. At 248 nm, all precursors lead to nearly thermal CN rotational distributions with rotational temperatures of approximately 1100 K in v = 0 and 800 K in v = 1. The vibrational distributions could not be characterized by the same temperatures. At 193 nm, contributions from two apparently different dissociation channels were observed. The CN rotational populations showed a narrow, strongly peaked distribution lying on a broad, approximately statistical distribution. For HNCS, this peak occurs near N = 10 suggesting dissociation from an excited state with a linear NCS skeleton. For the alkyl precursors, the peak occurs at very high rotational quantum number (N = 70) indicating an excited state with a bent NCS framework. Vibrational distributions with population out to v = 6 were observed. In all cases, the apparent statistical part of the rotational distribution and the vibrational distributions can be described by a prior function derived assuming that the internal modes of the alkyl substituent are not involved in any energy redistribution during the dissociation.