Triplet level

Figure Bl.16.3. Energy levels versus inter-radieal separation for a radieal pair. The lower part of the figrire shows tire S and T levels in the absenee of an external magnetie field while the mset shows the splitting of the triplet levels in the presenee of a magnetie field,...

Because the spin-orbit interaction is anisotropic (there is a directional dependence of the view each electron has of the relevant orbitals), the intersystem crossing rates from. S to each triplet level are different. 

Therefore, unequal populations of tlnee triplet levels results. The T, and basis fiinctions can be... 

As is the case with singlet states, absorption of light by the triplet can occur to produce higher triplet levels. We have previously seen how triplet-triplet absorption by flash photolysis is used as a tool in photochemistry. 

Photodimerization of isoprene has also been observed using ferrocene as sensitizerproduct distribution in this case was similar to that observed using high-energy photosensitizers. To account for this behavior, the following mechanism was proposed, where 7 indicates a triplet level of isoprene higher than the lowest triplet ( ) ... 

Fermi golden rule, 268 Filipescu, N., 291 Fisch, M. H., 307 Fischer, F., 379 Flash photolysis, 80-92 of aromatic hydrocarbons, 89, 90 determination of jsc, 228-230 determination of triplet lifetime, 240-242 energy of higher triplet levels, 219-220 flash kinetic spectrophotometry, 82, 83 measurement of triplet spectra, 81,82 nanosecond flash kinetic apparatus, 89 nanosecond flash spectrographic apparatus, 88... 

In practice, however, the situation is more complicated since some of the triplets may be excited to higher triplet levels (7 -> Tx) by the same wavelengths of light used to determine AOD. This results in a [A ]r less than the actual concentration depending upon the magnitude of the triplet molar absorptivity et. If et is known, a correction for Tx -> TX absorption can be made<63) ... 

Figure 5.9. Effect of spin-spin dipolar interaction and an external magnetic field on triplet levels.

In ruthenocene it also proved possible at 77 K to resolve the broad band containing the 12+ -> 1n, and 1Z+ -+ x4> transitions, but as for Fe(Cp)2 only one spin-forbidden d-d band, assigned as shown in Table 11, could be found, despite a spin-orbit coupling constant of the order of 1 kK. Note that although the 3I1 (on S4), 34 (o2 tr 5 3), and 3II (o2 n 6 3) levels are predicted (81) to be split by , %, and 31, respectively, abnormally large band widths would not be anticipated since only one component of each triplet level is capable of mixing with the nearby singlet states. 

From an inspection of the predicted intensities in Table 24 it is evident that absorptions due to triplet levels are likely to predominate within the other three d-ionisation bands, and first order ligand field theory gives the energies of these, relative to the 12+(a2 54)level, as 3IT(a2 tt 53) = 34>(a27r 53) = At + A2 - 9 B - 3 C, and 3Ila7r 54) =... 

Among the many excited singlet and triplet levels, 5i and Ti have distinct properties. They are in general the only levels from which luminescence is observed (Kasha rule) also most photochemical reactions occur from Sr or Ti. Here we discuss the characterization of the lowest triplet state by electronic spectroscopy. First we treat the theoretical background that allows the absorption spectra of conjugated systems to be described, and then we discuss the routes that lead to phosphorescence emission and Ti- - Sq absorption intensity. Details of the experimental methods used to determine triplet-triplet and singlet-triplet absorption spectra, as well as phosphorescence emission spectra are given in Chapters III, IV, and V. Representative examples are discussed. 

Triplet level Polarization Oscillator strength ) Radiative lifetimesi)... 

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