FEMTOSECOND INFRARED-SPECTROSCOPY - ULTRAFAST PHOTOCHEMISTRY OF IRON CARBONYLS IN SOLUTION

The photochemistry of cyclopentadienyliron dicarbonyl dimer in cyclohexane has been investigated with a novel femtosecond infrared spectrometer. Visible (580 nm) photolysis proceeds through an excited bound state that persists for about 1 ps. Dissociation occurs through more than one channel and is suggested to generate singly bridged and/or nonbridged dimers and homolytically cleaved species. Solvation of the nascent fragments apparently begins around 5 ps and nears completion around 10 ps. This delay in solvation may arise because visible excitation generates photoproducts with sufficient excess energy to inhibit complexation with the solvent at earlier times. Roughly half of the photodissociated dimers recombine geminately within almost-equal-to 20 ps, presumably through a singly bridged intermediate. Therefore, singly bridged photoproducts would not participate in photoinitiated bimolecular chemical reactions with diluted species.