Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules.

The πσ*‐mediated photochemistry of heteroaromatic molecules has provoked the investigation of the conical intersection dynamics. The Born–Oppenheimer approximation fails at the conical intersection where the S1 (ππ*) and S2 (πσ*) states cross. The nonadiabatic transitions are much influenced by the nuclear configuration of the reactive flux particularly in the curve‐crossing region encountered along the reaction pathway. In this article, we focus on the tunneling dynamics of phenols and thiophenols. The O (S)H bond cleavage occurs via tunneling through the barrier which is dynamically shaped by the upper‐lying S1/S2 conical intersection in terms of the couplings at the individual branching planes as well as along the (3N‐8) dimensional seam coordinates. State‐specific tunneling rates and their interpretation are given for phenol, substituted phenols, thiophenol, ortho‐substituted thiophenols, and benzenediols including their 1:1 water clusters. The completely orthogonal modes to the tunneling coordinate are very critical in the dynamic shaping of the reaction barrier. [ABSTRACT FROM AUTHOR]