Photodissociation dynamics of Mo(CO)6 at 266 and 355 nm: CO photofragment kinetic-energy and internal-state distributions

Abstract

The internal-state and kinetic-energy distributions of the CO photofragments from the 266 and 355 nm photolysis of Mo(CO)6 have been measured under collision-free conditions using vacuum-ultraviolet laser-induced fluorescence. The rotational-state distributions for CO(v″=0) and (v″=1) are well represented by Boltzmann distributions with effective rotational ‘‘temperatures’’ of Tr(v″=0)=950±70 K and Tr(v″=1)=935±85 K for 266 nm and Tr(v″=0)=750±70 K and Tr(v″=1)=1150±250 K for 355 nm photolysis. The CO(v″=1/v″=0) vibrational-state ratios for 266 and 355 nm photolysis are 0.19±0.03 and 0.09±0.02, respectively. The Doppler-broadened CO photofragment line shapes indicate that the translational energy distributions are isotropic and Maxwellian. There is no photolysis-laser wavelength or internal-state dependence to the extracted translational ‘‘temperatures.’’ The observed energy partitioning and kinetic-energy distributions are inconsistent with an impulsive ejection of a single CO ligand. CO photofragment line shapes for 266 nm photolysis are not consistent with a mechanism involving the repulsive ejection of the first CO ligand, followed by the statistical decomposition of the Mo(CO)5 fragment. While phase-space theories do not predict quantitatively the energy disposal, the photodissociation mechanism appears to be dominated by statistical considerations. The results also suggest that the photodissociation of Mo(CO)6 at 266 and 355 nm involves a common initial ‘‘state’’ and that similar exit channel effects are operative.