193 nm laser photofragmentation time-of-flight mass spectrometric study of HSCH2CH2SH

The kinetic energy release spectra for SH resulting from the 193 nm laser photofragmentation of HSCH2CH2SH have been measured. On the basis of the observed maximum kinetic energy for the formation of HS+CH2CH2SH, a value of 74±2 kcal/mol is derived for the bond dissociation energy of HS–CH2CH2SH at 0 K [D0(HS–CH2CH2SH)]. Angular distribution measurements for SH yield an anisotropic parameter β=−0.4±0.1 for the HS+CH2CH2SH channel, indicating that the C–S bond fission is fast with respect to molecular rotation. The energetics for the formation of HS+CH2CH2SH from HSCH2CH2SH have been investigated using the Gaussian-2 (G2) and G2(MP3) ab initio quantum chemical procedures. The G2/G2(MP3) calculations give a prediction of 72.5 kcal/mol for D0(HS–CH2CH2SH), in excellent agreement with the experimental value. Ab initio first-order configuration interaction calculations have also been made to examine the possible excited state of HSCH2CH2SH involved in the photodissociation process and to rationalize the observed angular distribution for the HS+CH2CH2SH channel.