VIBRATIONAL IR-MULTIPHOTON EXCITATION OF THIIRANE-1-OXIDE (C2H4SO) AND D-THIIRANE-1-OXIDE (C2H3DSO)

We report the IR-laser-induced dissociation of C2H4SO and of C2H3DSO, which was synthesized for the first time. After multiphoton excitation in the frequency range of the SO chromophore (with a large band stren gth of G = 2.4 pm(2) for C2H4SO and 2.8 pm(2) for C2H3DSO) in the 1060 -1090 cm(-1) range of the CO2 laser the product analysis was carried o ut by static yield measurements using quantitative IR-spectroscopy of ethylene (C2H3D, C2H4). Effective laser chemical rate constants k(I)(s t) = (0.70+/-0.38) cm(2) J(-1) for C2H3DSO with excitation at ($) over tilde nu(R28) = 1083.48 cm(-1) and (0.52+/-0.14) cm(2) J for C2H4SO w ere obtained from a fit to the fluence dependence of the photochemical primary yields. A nonlinear intensity dependence of the apparent prod uct yield (P-app) was found by using different temporal pulse profiles (singlemode, mode-locked and multimode pulses) at 1083.48 cm(-1) (9R2 8) for C2H4SO and at 1082.30 cm(-1) (9R26) for C2H3DSO in static yield measurements and lime-resolved experiments. FTIR measurements were pe rformed to assign the fundamentals of C2H3DSO, which are compared with the harmonic frequencies calculated using GAUSSIAN 92 at MP2 level wi th different basis sets.