Vibrational structure of trifluoromethylthiobenzene (C6H5SCF3) on the S-1 state has been investigated by resonance-enhanced two-photon ionization spectroscopy and nature of predissociation dynamics is inferred from homogeneously broadened spectral features. As C6H5SCF3 adopts a nonplanar structure in both the S-0 and S-1 states, the effective adiabatic barrier generated by avoided crossing of optically bright bound S-1 (pi pi*) and dark-repulsive Sy (pi sigma*) surfaces along the reaction coordinate is significantly lowered, giving the S-1 lifetime of similar to 300 fs. This experiment demonstrates that the molecular structure spanned by the reactive flux near the curve-crossing region dictates reaction rate as well as nonadiabatic transition probability. (C) 2016 Elsevier B.V. All rights reserved.