The competition between laser selective dissociation of the axial Co-CO bond and intramolecular energy redistribution in HCo(CO)(4) is investigated. Our approach is based on an ab initio calculation of the Cartesian reaction surface Hamiltonian along the Co-CO bond distance using density functional theory. The substrate degrees of freedom are treated within the harmonic approximation. We find only two modes which are strongly coupled to the dissociation reaction, one which can be approximately described as an H-Co stretching vibration while the second one is an umbrella type vibration of the equatorial carbonyls. The region of validity for harmonic motion of the substrate normal modes is explored.