  The excitation of vibrational modes in molecules affects the outcome of
chemical reactions, for example by providing molecules with sufficient energy
to overcome activation barriers. In this work, we introduce a quantum algorithm
for simulating molecular vibrational excitations during vibronic transitions.
We discuss how a special-purpose quantum computer can be programmed with
molecular data to optimize a vibronic process such that desired modes get
excited during the transition. We investigate the effect of such excitations on
selective bond dissociation in pyrrole and butane during photochemical and
mechanochemical vibronic transitions. The results are discussed with respect to
experimental observations and classical simulations. We also introduce
quantum-inspired classical algorithms for simulating molecular vibrational
excitations in special cases where only a limited number of modes are of
interest.
