Doublet excited state process

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

In a very important study of the quartet-doublet reactivity question,72 it was found that ligand-field irradiation of [Cr(CN)6]3 in degassed dimethylformamide results in both phosphorescence from the doublet and substitution of cyanide. In air-saturated solution, however, phosphorescence is quenched completely while the photoreaction is unaffected. The two processes appear to be uncoupled and thus originate from different excited states. The most straightforward conclusion is that the lowest quartet excited state in [Cr(CN)6]3 is the sole precursor to photoreaction. 

This operation correlates the ground and excited states on both surfaces. The two-level charge-induced interchange of the conformers can occur on a timescale of a few picoseconds, which is typical for the resonant photoionization process [35], The dynamics of such a process, 0)° -> 1)+1 and 1)° -> 0)+1, is monitored in real time by the change in the anchoring A-N stretch, equal to Av(Au-N) = 145, 165 (due to the appearance of the A-N stretch doublet), and by the disappearance of the vibrational mode -v(N-H - N) (see Table 3) using, e.g. time-resolved picosecond UV/IR pump-probe ionization depletion spectroscopy [35]. 

The correlation of the potential surfaces to the product OH seems obvious. The asymmetric excited state correlates to the asymmetric A-doublet, whereas the symmetric ground state correlates to the symmetric A-doublet. Conservation of electronic symmetry in the fragmentation predicts the formation of OH exclusively in the asymmetric A-doublet state. Conservation of electronic symmetry implies that the motion proceeds along the same potential surface and that transitions to other potential surfaces are negligible. This so called adiabatic behaviour is expected to hold for most molecular processes. It seems immediately clear that the origin for the selective population of A-doublet states is due to adiabatic behavior. 

The TBN excited state is of a" symmetry where the n lobes are perpendicular to the molecule rotation plane. The conservation of symmetry would cause the antisymmetric A doublet component of the NO fragment to be highly populated relative to the symmetric A doublet component provided that the dissociation process is fast and planar. An indication to the planarity of the TBN photofragmentation process is found from the ali ment factor derived in the next section. It has been shown that in a state the Q lines probe the H" A doublet levels... 

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