A TD-DFT study on dissociative loss of the axial and equatorial carbonyl for HCo(CO)4

In this work we explore two probably competitive photodissociation pathways for the loss of an axial and equatorial carbonyl ligand in HCo(CO)4 by means of TD-DFT calculations with the ADF program. The potential energy profiles for several low-lying singlet and triplet states along the two dissociation pathways are investigated upon vertical transitions. The calculations suggest that the equatorial homolysis of carbonyl plays an important role in the photodissociation processes. Accordingly, DFT studies on the ground state structure of HCo(CO)3 reveal that for each dissociation channel there is a stable singlet state, corresponding to C3v and Cs symmetry, respectively. Subsequently, a small energy barrier of 6.0 kJ/mol is found for isomerization of HCo(CO)3 from the C3v conformation to the Cs one. In addition, the absorption spectra of HCo(CO)4 in the UV/vis region by the TD-DFT method are compared with the available experimental and theoretical results. The calculated spectrum positions of the starting absorption and the most intense absorption are in good agreement with the experimental observation.