| Transient infrared absorption spectra of the coordinatively unsaturated species generated via excimer laser photolysis of gas phase Fe(CO)(,5), Cr(CO)(,6) and Mn(,2)(CO)(,10) are presented and discussed. The photofragments produced upon 351-, 248- and 193-nm photolysis are characterized. These coordinatively unsaturated photofragments are typically formed with significant amounts of internal excitation. The results indicate that the gas phase structure of the (ground state) photofragments are the same as those observed in condensed phase experiments. Rate constants for the reaction of these fragments with CO (or, in the case of Mn(CO)(,5), with another Mn(CO)(,5) radical) are found to be nearly gas kinetic collisional rate constants if the reaction is not spin forbidden. The rate constants for the reaction of (C(,2v)) Fe(CO)(,4), (C(,3v)) Fe(CO)(,3) and Fe(CO)(,2) with CO are (3.5 (+OR-) 0.9) x 10('10)-, (1.3 (+OR-) 0.2) x 10('13)- and (1.8 (+OR-) 0.3) x 10('13)-cm('3)mol('-1)sec('-1), respectively. The rate constants for the reaction of (C(,4v)) Cr(CO)(,5), (C(,2v)) Cr(CO)(,4) and (C(,3v)) Cr(CO)(,3) with CO are (1.5 (+OR-) 0.3) x 10('13)-, (2.4 (+OR-) 0.3) x 10('13)- and (1.8 (+OR-) 0.3) x 10('13)-cm('3)mol('-1)sec('-1), respectively. Finally, the rate constant for the Mn(CO)(,5) radical-radical recombination reaction is near gas kinetic, while that for the reaction of Mn(,2)(CO)(,9) with CO is (2.4 (+OR-) 0.5) x 10('9)cm('3)mol('-1)sec('-1).; To a first approximation, the number of ligands lost by an absorbing molecule can be predicted via consideration of bond dissociation energy versus input photon energy. It is found, however, that the nature of the electronic state populated can have profound effects on the nature of the fragments produced upon photolysis. For the Mn(,2)(CO)(,10) and Fe(CO)(,5) systems, the results indicate that different photochemical pathways are accessed upon 193 nm- and 351 nm-photolysis. |
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