Electronic levels singlet

In this article we have reviewed the results of a joint spectroscopic and morphological investigation of -sexilhienyl (T(J. The lowest singlet electronic level, which is assigned to I B , splits in the single crystal into four crystalline levels. The structure of the exciton band is investigated by the combined absorption and... 

The fluorescence and phosphorescence spectra of a complex molecule are generally discussed by reference to an energy level diagram such as that shown in Figure 1. Absorption of light raises the molecule from the ground state to one of the upper electronically excited singlet states. At... 

Figure 11.2—Energy diagram showing the rotational, vibrational and electronic states of a molecule. On the scale of this diagram, the rotational and vibrational levels should be comparatively closer than the electronic levels because their relative values are in the order of 1000 50 1. The framed section shows, in the form of an energy diagram, the absorption of a photon. This figure represents the promotion of an electron from an occupied orbital (HOMO) to an unoccupied orbital (LUMO) giving rise to a singlet, which rapidly evolves into a more stable triplet state.

Phosphorescence corresponds to a different relaxation process. After the absorption phase, corresponding to the transfer of one electron into the Si level (singlet state), a spin inversion can occur if vibrational relaxation is slow, leading the electron to a T, state (triplet state) that is slightly more stable. Flence, return to the ground electronic state will be slower because it involves another spin inversion for this electron. For this reason, radiative lifetimes for phosphorescence can be up to 108 times greater than for fluorescence. 

Fig. 2. Sharp emission from Ln111 ions due to the small offset of the electronic levels as shown from the configurational coordinate diagram (right) as a comparison, the case of an organic molecule is depicted on the left ( So = singlet ground state, 1S = singlet excited state).

Upon collisional deactivation tra i-azoalkanes isomerize to the cis form. (This reaction is the only known synthetic route to m-azoalkanes.) The process is reversible, but — at least in the liquid phase — occurs only in direct photolysis or singlet sensitized photolysis and not in triplet sensitization. Decomposition in the condensed phase appears to exhibit similar behavior. These kinetic features cannot be rationalized in terms of the two electronic levels predicted by mo calculations and various other alternatives have been suggested as will be discussed below. 

The difference arises in that Brewer and Rosenblatt (7 ) approximated the CrO electronic levels with Cr electronic levels. The latter has a singlet ground state and many levels lying below 600 cm". ... 

Recent MO calculations ( ) predict a singlet ground state with no low-lying electronic levels, and are supported by the x-ray emission ( ) and absorption (22, 2 ) spectra of gaseous SFg. Gianturco (28) has presented a description of the electronic properties. 

The electronic levels, bond angle and stretching frequencies are from infrared and emission spectra of TiOg isolated in rare-gas matrices ( 14). We assume the emission at 5295 A to be a forbidden triplet-singlet transition due to its similarity with CeOg... 

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