Ultraviolet laser photolysis: Primary photochemistry of Fe(CO)5 in PF3

Abstract

We have studied the photolysis of mixtures of Fe(CO)₅ and PF₃ with a KrF laser operating at 248 nm. The product yields of Fe(CO)₂(PF₃)₃, Fe(CO)₃(PF₃)₂, and Fe(CO)₄PF₃ have been measured as a function of laser fluence and mixture composition. A simple kinetic model appears to explain semiquantitatively the observed dependence of product yield upon mixture composition. This model has allowed us to determine that the primary photochemical yields at 248 nm for the fragments Fe(CO)₂, Fe(CO)₃, and Fe(CO)₄ over the fluence range 0.1–200 mJ/cm² are 0.55, 0.35, and 0.10, respectively, independent of laser fluence. This fragmentation results from a simple one‐photon absorption process. We have found that CO ligands are exchanged readily in collisions of the above fragments with Fe(CO)₅, with a bimolecular rate constant relative to that for trapping by PF₃ of k_M/k_T=4. We have also found that these primary photofragments react with Fe(CO)₅ to form unobserved products with a rate constant (relative to that for trapping by PF₃) of k_Q/k_T=7.