Charge doublet state

If a charge exchange process, A + + B- A -f- B +, occurs when the distance between the two particles is large, we expect that no transfer of translational energy takes place in the reaction and that the same selection rules govern the ionization as in spectroscopic transitions. This means that if the molecule B is in a singlet state before the ionization, the ion B + will be formed in a doublet state after ionization of one electron without rearrangements of any other electrons, at least for small molecules. 

Nevertheless, there exist a number of free radicals (25 +1=2, doublet state), for which ESR measurements suggest non-classical structures as a result of homoconjugative (homoaromatic) interactions. In all cases of radical homoaromaticity considered so far, the radicals in question are actually radical cations. This again emphasizes the important role of a positive charge in connection with homoconjugation36. 

The ionization potential is determined by removing an electron from the highest occupied molecular orbital (HOMO). For an even n cluster, in a singlet state, the electron which is removed will see a greater nuclear charge than will an electron in the HOMO of an odd n cluster in a doublet state. This results because the nuclear charge for a closed shell orbital is only partially screened by the other electron in that orbital. In contrast, an odd electron in what is probably a more diffuse HOMO... 

Excitation of the NI anion radical within ANI+-NI -PI with a 480 nm laser pulse rapidly forms the ANI+ NI -PI excited doublet state. Its electronic configuration is analogous to that in Figure 4(b). There are two pathways for decay from this excited state charge recombination back to yield the ANI excited state or charge shift to PI. The driving force for each of these paths is nearly identical, and... 

Figure 1. A typical excited-state diagram for a hexacoordinated Cr(lll) complex, where represents the ground state, and Qj the lower energy quartet, ligand-field state CT a charge-transfer state, ISC intersystem crossing and D the lowest-energy doublet state.

K.F. Dunn, B.J. Gilmore, F.R. Simpson, H.B. Gilbody, He(2 S) and He formation in fast charge-changing collisions and evidence for a long-lived doublet state of He, J. Phys. 

X = 8000 cm" ). It is seen that the charge recombination process leading to the Cr(ni) doublet state is expected to be in the nearly activationless regime, whereas that leading to the ground state is likely to lie deep into the "inverted region" of electron transfer (section 1.3.2). In terms of radiationless transition theory, the excited-state charge recombination is favored by its... 

Arenas, J. F, Lopez-Tocon, I., Castro, J. L, Centeno, S. R, Lopez-Ramirez, M. R., and Otero, J. C. [2005] Resonant charge transfer on the nanoscale Studying doublet states of adsorbates by surface-enhanced Raman scattering,/. Raman Spectrosc., 36, 515-521. 

---