Ethylene dynamics would be the prototypical example with its twisted-pyramidalized conical intersection funneling the excited-state population within less than 100 fs. The second type-exemplified by S3-excited n-AIH + -occurs when the molecule remains at moderate gaps, where the hopping probability is small but the hopping opportunities numerous (Figure -right). These two regimes can also be respectively identified as the strong and weak coupling limits of Engels and Jortner. This short paper further develops how ultrafast internal conversion can occur in this second scenario. We work in the frame of instantaneous probabilities, in which the probability of a nonadiabatic transition between electronic states is a function of time, such as in the fewest switches surface hopping (FSSH). An alternative would be to work with global nonadiabatic frameworks, which evaluate the total probabilities that the molecule would end in each state, just like in the Landau-Zener model. Another alternative would be to employ Fermi's Golden rule to get probability per unit of time (rate). Nevertheless, working with instantaneous probabilities can directly connect the discussion to FSSH surface hopping simulations. )