Diode laser probes of the product distribution of coordinatively unsaturated iron carbonyls produced following excimer laser photolysis of Fe(CO)₅ in the gas phase

The distributions of photoproducts created by single photon photolysis of Fe(CO)₅ at 193, 248, and 351 nm have been determined by using a tunable infrared diode laser to monitor the concentration of Fe(CO)₅ consumed in reactions with each photoproduct. The relative concentrations of the iron carbonyl photofragments that form are as follows: on 193-nm photolysis, 90 ± 5% Fe(CO)₂ and 10 ± 5% Fe(CO); on 248-nm photolysis, 64 ± 7% Fe(CO)₃ and 36 ± 7% Fe(CO)₂; and on 351-nm photolysis, 39 ± 5% Fe(CO)₄ and 61 ± 5% Fe(CO)₃. A pressure dependence of the 248-nm product yield is observed, and the reported branching ratio is for 3 Torr of total pressure. Peak absorption coefficients of these species are reported. In addition to these products, which are produced in their ground electronic states, species best assigned as excited electronic states of Fe(CO)₄ and Fe(CO)₃ are produced following 351- and 248-nm photolysis, respectively. These product distributions are compared to those reported in other studies, and evidence is presented that for at least some of the wavelengths employed in this study the dissociation of Fe(CO)₅ involves multiple potential energy surfaces.