Singlet energy

The energy per atom consists of kinetic energy, singlet, and pair potential terms,... 

In 95% ethanol, 4,4 -BPDC shows a strong fluorescence and relatively weaker phosphorescence (relative intensity 10-2 times the fluorescence). This indicates, though perhaps unexpected, the lowest energy singlet state is a (ir,ir ) state... 

FIGURE 2. Some configurations describing the low-energy singlet states of linear polyenes... 

The electronic states of the molecule and their relative energies. Singlet electronic states are denoted by S0, Si, S2, etc. and triplet... 

According to Fig. la, state is likely to be the lowest-energy singlet, because both electrons lie in the lower-energy a orbital. However, the relative... 

Parasuk and Cramer s calculations indicate that triplet vinylnitrene is 15 kcal/mol more stable than the lowest energy singlet state. The lowest energy singlet state is open shell and resembles a 1,3-biradical. 

The only head-to-head polymer which has been examined for excimer fluorescence is polystyrene 25). Unfortunately, the synthetic route to this polymer leaves a number of stilbene-based structures in the sample, which have a lower-energy singlet state than either PS monomer (285 nm) or excimer (330 nm). Thus, fluorescence from these intrinsic stilbene traps was seen in the spectra of head-to-head PS in pure films and, to a lesser extent, in fluid solution. In the latter, the fluorescence of PS monomer was predominant, and the small amount of stilbene fluorescence was increased when a nonsolvent (methanol or cyclohexane) was added to the 2-methyl-tetrahydrofuran solution. In films of the polymer, stilbene fluorescence was the major spectral band, although some PS excimer fluorescence was also present in the spectrum. No monomer fluorescence at 285 nm was detected from films. Given the impure nature of the head-to-head PS sample, no conclusions on excimer formation in these systems could be drawn. 

Direct irradiation of unconjugated olefins yields very high-energy singlets which cross over to the triplet manifold very inefficiently, so... 

FIGURE 1. Lowest-energy singlet (S) and triplet (T) state of a carbene... 

Termination of the autoxidation chain process occurs as peroxyl radicals couple to yield non-radical products. This reaction takes place through an unstable tetroxide intermediate. Primary and secondary tetroxides decompose rapidly by the Russell termination mechanism to yield three non-radical products via a six-membered cyclic transition state (Fig. 95). The decomposition yields the corresponding alcohol, carbonyl compound, and molecular oxygen (often in the higher energy singlet oxygen state) three... 

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