Different Photodissociation\nMechanisms in Fe(CO)<sub>5</sub> and Cr(CO)<sub>6</sub> Evidenced\nwith Femtosecond Valence\nPhotoelectron Spectroscopy and Excited-State Molecular Dynamics Simulations

Measured and calculated time-resolved photoelectron spectra\nand\nexcited-state molecular dynamics simulations of photoexcited gas-phase\nmolecules Fe(CO)<sub>5</sub> and Cr(CO)<sub>6</sub> are presented.\nSamples were excited with 266 nm pump pulses and probed with 23 eV\nphotons from a femtosecond high-order harmonic generation source.\nPhotoelectron intensities are seen to blue-shift as a function of\ntime from binding energies characteristic of bound electronic excited\nstates via dissociated-state energies toward the energies of the dissociated\nspecies for both Fe(CO)<sub>5</sub> and Cr(CO)<sub>6</sub>, but differences\nare apparent. The excited-state and dissociation dynamics are found\nto be faster in Cr(CO)<sub>6</sub> because the repopulation from bound\nexcited to dissociative excited states is faster. This may be due\nto stronger coupling between bound and dissociative states in Cr(CO)<sub>6</sub>, a notion supported by the observation that the manifolds\nof bound and dissociative states overlap in a narrow energy range\nin this system.