Triplet simple

Figure 7.10 (a) A simple triplet and (b) a compound triplet in the spectrum of an alkaline earth... 

The simple triplet-triplet quenching mechanism requires that at low rates of light absorption the intensity of delayed fluorescence should decay exponentially with a lifetime equal to one-half of that of the triplet in the same solution. Exponential decay of delayed fluorescence was, in fact, found with anthracene, naphthalene, and pyrene, but with these compounds the intensity of triplet-singlet emission in fluid solution was too weak to permit measurement of its lifetime. Preliminary measurements with ethanolic phenanthrene solutions at various temperatures indicated that the lifetime of delayed flourescence was at least approximately equal to one-half of the lifetime of the triplet-singlet emission.38 More recent measurements suggest that this rule is not obeyed under all conditions. In some solutions more rapid rates of decay of delayed fluorescence have been observed.64 Sufficient data have not been accumulated to advance a specific mechanism but it is suspected that the effect may be due to the formation of ionic species as a result of the interaction of the energetic phenanthrene triplets, and the subsequent reaction of the ions with the solvent and/or each other to produce excited singlet mole-... 

The fine structure of a 3P — S transition of an alkaline earth metal is illustrated in Figure 7.10(a). The A J selection rule (Equation 7.22) results in a simple triplet. (The very small separation of 23P1 and 23P2 in helium accounts for the early description of the low-resolution spectrum of triplet helium as consisting of doublets .)... 

This mechanism corresponds to one considered earlier by Dannenberg 12SK The consideration of a simple triplet energy transfer from the ferrocene T% (54 kcal/mole) [see section B] to piperylene [7T = 56.9 for the cis isomer and 58.8 kcal/mole for the trans isomer] has been rejected, since ferrocene was thought to behave like a high-energy sensitizer 128,129). However, in trans-1.2-dimethylcyclohexane it was shown to... 

At room temperature, protons (a) are magnetically equivalent and give a simple triplet with 1 2 1 intensity ratios. Below 261°K the spectra of individual rotamer forms begin to resolve. It is possible to 9... 

We close this section by noting that Knight et al. have reported ESR spectra of more simple triplet radical pairs of and D - D trapped in rare gas... 

CARS can be resonantly-enhanced electronically when either the pump, Stokes or the CARS frequency Itself coincides with an electronic transition in the probed species. Stokes resonances are weighted by the excited vibrational state involved in the Raman resonance and this enhancement is generally weak even at flame temperatures. More typically one tries to achieve primary resonance with the pump laser. In so doing, Stokes resonances are automatically satisfied. The strength of the resonance scales as the product of the four dipole matrix elements Involved with each field in the wave mixing process. Thus only certain transitions tend to be enhanced leading in most cases to a simplification of the CARS spectrum. In the case of the combustion relevant OH molecule under study in our laboratory, a simple triplet spectrum is predicted since each Raman-resonant, downward Stokes transition must satisfy the appropriate dipole selection mles for strong electronic enhancement as shown in Fig. 10. ... 

Several simple 1,3-biradicals have been directly observed spectroscopically. Photolysis of 2,3-diazabicyclo[2.2.1 ]heptene in a frozen solvent at temperatures below 10 K produced a simple biradical, 1,3-cyclopentanediyl, the triplet state of which was directly observed by Closs using EPR spectroscopy (Eq. 11.85). Similarly, a series of substituted 1,3-cyclobutane-diyls was produced (Eq. 11.86), showing that substituent effects on simple, triplet biradicals mirror those of conventional free radicals. 

FIGURE 15.51 In 2-chloropropanoic acid, each methylene group appears as a simple triplet. Notice that the signals for these coupled hydrogens lean toward each other. 

Also, the methylene protons of the alkenyl side chain at C-5 absorb at different S values in trans isohumulone, forming an AB-spin system. In cis isohumulone a simple triplet signal is observed. 

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