By examining the competition between fragmentation and photoionization of selectively photoexcited Fe(CO)5in a pulsed jet, we have been able to estimate wavelength dependent upper limits for excited state lifetimes. These range from 0.6 to 1.0 ps over the region from 290 to 310 nm. The nascent CO produced by this dissociation and subsequent multiple fragmentation is detected with rovibronic specificity by twohyphen;photon resonant fourhyphen;photon ionization. Results on dynamics and lifetimes favor a dissociation model involving an unbound lowest ligand field state densely mixed with higherhyphen;lying ligandhyphen;field and charge transfer states. We also report the observation of highly efficient ionndash;molecule fragmentation reactions of Fe(II) with cold Fe(CO)5, in which fragmentation branching ratios depend critically on the Fe(II) states produced by preceding resonancehyphen;enhanced twohyphen;photon ionization of free Fe atoms.
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