High-resolution time-of-flight measurements of H atom products from photolysis of phenol, 4-methylphenol, 4-fluorophenol, and thiophenol, at many UV wavelengths (λ phot ), have allowed systematic study of the influence of ring substituents and the heteroatom on the fragmentation dynamics. All dissociate by X H (X = O, S) bond fission after excitation at their respective S 1 ( 1 ππ*)– S 0 origins and at all shorter wavelengths. The achieved kinetic energy resolution reveals population of selected vibrational levels of the various phenoxyl and thiophenoxyl coproducts, providing uniquely detailed insights into the fragmentation dynamics. Dissociation in all cases is deduced to involve nuclear motion on the 1 πσ* potential energy surface (PES). The route to accessing this PES, and the subsequent dynamics, is seen to be very sensitive to λ phot and substitution of the heteroatom. In the case of the phenols, dissociation after excitation at long λ phot is rationalized in terms of radiationless transfer from S 1 to S 0 levels carrying sufficient O H stretch vibrational energy to allow coupling via the conical intersection between the S 0 and 1 πσ* PESs at longer O H bond lengths. In contrast, H + C 6 H 5 O(X 2 B 1 ) products formed after excitation at short λ phot exhibit anisotropic recoil-velocity distributions, consistent with prompt dissociation induced by coupling between the photoprepared 1 ππ* excited state and the 1 πσ* PES. The fragmentation dynamics of thiophenol at all λ phot matches the latter behavior more closely, reflecting the different relative dispositions of the 1 ππ* and 1 πσ* PESs. Additional insights are provided by the observed branching into the ground (X 2 B 1 ) and first excited ( 2 B 2 ) states of the resulting C 6 H 5 S radicals.