Quantifying rival bond fission probabilities following photoexcitation: C-S bond fission in t-butylmethylsulfide

We illustrate a new, collision-free experimental strategy that allows determination of the absolute probabilities of rival bond fission processes in a photoexcited molecule – here t-butylmethylsulfide (BSM). The method combines single photon (‘universal’) ionization laser probe methods, simultaneous imaging of all probed fragments (multi-mass ion imaging) and the use of an appropriate internal calibrant (here dimethylsulfide). Image analysis allows quantification of the dynamics of the rival BSM and BSM bond fission processes following ultraviolet (UV) excitation of BSM and shows the former to be twice as probable, despite the only modest (~2%) differences in the respective ground state equilibrium C–S bond lengths or bond strengths. Rationalising this finding should provide a stringent test of the two close-lying, coupled excited states of 1Au0027 symmetry accessed by UV excitation in BSM and related thioethers, of the respective transition dipole moment surfaces, and of the geometry dependent non-adiabatic couplings that enable the rival C–S bond fissions.