States‐Resolved Detection of the NO Fragments From Photodissociation of Co(CO) ₃ NO in Two Metal‐to‐Ligand Charge‐Transfer Bands

The photodissociation dynamics of Co(CO) ₃ NO in the metal‐to‐nitrosyl (NO) ligand charge‐transfer (MLCT(NO)) band were investigated by gas‐phase pump‐probe experiments and theoretical calculations. The results at the photolysis wavelength of 380 nm were compared with those of the MLCT(CO) photodissociation dynamics to differentiate ligand loss mechanisms initiated by charge‐transfer to different ligands. The rotational and vibrational state populations of the NO fragments exhibited an imperfectly thermalized distribution, as evidenced by comparisons with data at the photolysis wavelengths of 450 nm (MLCT(NO) band) and 225 nm (MLCT(NO) band). The scattering distributions of the NO photofragments measured by ion‐imaging exhibited anisotropic angular distributions, indicating that fast dissociation competes with internal energy redistribution. We ascribed the similar translational energy releases in the MLCT(NO) and MLCT(CO) photolysis to dissociation from common electronic states with both charge‐transfer excitations followed by electronic relaxations. The experimental results were interpreted in terms of indirect NO loss via triplet excited states based on the quantum chemistry calculations. The distinct dynamics of the two charge‐transfer bands exemplify the importance of the charge density on a dissociating ligand in heteroleptic metal complexes upon photoexcitation.