“…However, we must address the possibility that the dark upper state could be populated by vibronic interactions, which would then weaken the expected left-right asymmetry in the observed distributions since the asymmetry in the MFPADs for the lower and upper states would, when summed, cancel each other. To address this effect, it is convenient to work in the diabatic representation, for which we use a two-state model in a simplified one dimensional picture considering only the asymmetric stretch nuclear coordinate R [14,15], The diagonal adiabatic potential matrix H ', whose elements are the computed lower and upper n* states, can be transformed into a diabatic potential matrix Hrf, whose diagonal elements are the diabatic potentials and the off-diagonal elements are the electronic coupling elements. The transformation is given by…”