UV Photodissociation Dynamics of CD3SOCD3:  Photofragment Translational and Internal Energy Distribution

The photodissociation of CD3SOCD3 (DMSO-d 6) has been studied at four different wavelengths in the UV region (204−227 nm) using resonance enhanced multiphoton ionization (REMPI) and time-of-flight mass spectrometry (TOFMS) to measure TOF profiles and rotational and vibrational REMPI spectra of the CD3 photoproduct. Three dissociation channels producing CD3 fragments have been identified. The major primary channel proceeds via internal conversion to the ground state followed by unimolecular decomposition, and it is characterized by an isotropic statistical translational energy distribution. Internally hot CD3SO(X̃) fragments subsequently decompose over an exit barrier (45 ± 2 kJ mol-1) to produce CD3 and SO. Another primary channel results from a fast dissociation (direct dissociation or predissociation) that yields anisotropic CD3 and presumably electronically excited CD3SO(Ã) fragments with β = 0.30 ± 0.05. In this last case, the fraction of available energy channeled into translation (〈f t〉 ≈ 0.62) is consistent with a soft impulsive model. The measured rotational spectra confirm the results obtained from the TOF profiles simulations.