Near UV photodissociation of dimethyl sulphide: a direct mechanism on the second absorption band

The technique of resonance-enhanced multiphoton ionisation with time-of-flight mass spectrometry (REMPI–TOFMS) has been used to study the photodissociation of fully deuterated dimethyl sulphide (CD3SCD3) following excitation within its second absorption band (λ ≈ 200 nm). Analysis of TOF profiles of the nascent CD3 products indicate a strongly anisotropic photodissociation with more than 80% of the available energy appearing as fragment recoil translation. A negative anisotropy parameter is found, β = −0.9 ± 0.1, corroborating the recent spectroscopic assignment of the second absorption band to a 1 B 1 ← X ˜ 1 A 1 transition [W.R. Mason, J. Phys. Chem. 100 (1996) 8139]. The large fraction of energy found in product translation, independent of excitation energy, indicates that photodissociation on the second absorption band occurs directly, via only one excited electronic state, in contrast to the situation on the first absorption band where two strongly coupled excited states are involved.