Photofragment spectroscopy of cobalt tricarbonylnitrosyl and its trialkylphosphine derivatives

The photodissociation of gaseous Co(CO)3(NO) and Co(CO)2(NO)(PX3), where X=CH3, C2H5, n-C3H7, and n-C4H9 has been investigated near 225 nm by state-selective multiphoton ionization detection of nitric oxide fragments. The observed NO photofragment rotational distributions in v=0 are approximately Boltzmann, and the characteristic temperature decreases with increasing size of the phosphine ligand. The yield of photofragments appearing within the 10 ns detection time scale also decreases with increasing molecular size. An analogous effect is observed for the v=1/v=0 vibrational population ratio of the NO photoproducts. These results show that intramolecular energy transfer is fast compared with scission of the Co–NO bond. A dissociation model is proposed involving initial loss of CO followed by loss of other ligands via an RRKM-like process.