Chromium complexes, absorption excited states

In summary, spectroscopic studies show that at low temperatures higher excited states of chromium(III) complexes undergo rapid internal conversion to the metastable T2g or 2Eg levels. Intersystem crossing from the 4T2g to the aEg level occurs with near unit efficiency in many chromium(III) complexes. Phosphorescence competes, usually unfavorably, with radiationless decay from the 2Eg state. Studies of the excited states of Mo(III), (4d)3, based on absorption spectra of its complexes in solution, have recently been reported.134-137... 

Transient absorption measurements have recently been recorded from the organometallic species chromium hexacarbonyl in ethanol solution [94], Absorption of a 65-fs, 310-nm excitation pulse was followed by measurement of excited-state absorption of a 65-fs, 480-nm probe pulse. The data shown in Figure 14 indicate a rapid nonexponential decay at short times followed by a gradual exponential rise. The slower feature was observed previously [95] and is known to correspond to the solvent complexation of Cr(CO)5 to yield Cr(CO)j(MeOH). The initial feature, which is observed at other probe wavelengths as well, is believed to correspond to the initial ligand loss reaction. Note that this case is different from ICN in that the initially excited wavepacket is not on the side of the Sj potential but rather (as is clear from the molecular symmetry) on a local potential maximum. The wavepacket must then spread that is, dissociation along either direction is equally likely. The rapid nonexponential decay was analyzed in terms of classical kinematics along a dissociative potential. 

Chromiumfiiij.—Papers concerned with the kinetics and mechanisms of chromium(in) complexes are reviewed in the Inorganic Reaction Mechanisms Specialist Periodical Report Reviews of the absorption and emission spectra chromium(iii) complexes are reviewed in the Inorganic Reaction Mechanisms published. A model based on the antibonding properties of excited electronic states has been developed which correctly predicts the types of photoreaction and relative quantum yields of chromium(iii) and other transition-metal complexes. ... 

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