Excited species, from atom transfer reactions

The flame reactions of alkali metal vapors (Li, Na, Cs) with nitrogen trifluoride between about 500 and 1000 K and at a few Torr show strong chemiluminescence. The emission results from electronically excited alkali metal atoms. Photon yields of up to 3% were measured. The excitation mechanism was assumed to involve the formation of an excited species and the transfer of energy from this species to the alkali metal atom (A) according to the simplified sequence [1,2] A +NF,->AF(v) +NF,, ... 

Bimolecular reactions with paramagnetic species, heavy atoms, some molecules, compounds, or quantum dots refer to the first group (1). The second group (2) includes electron transfer reactions, exciplex and excimer formations, and proton transfer. To the last group (3), we ascribe the reactions, in which quenching of fluorescence occurs due to radiative and nonradiative transfer of excitation energy from the fluorescent donor to another particle - energy acceptor. 

Apart from the thermal oxidation-reduction reactions involving metal ions in different valency states, discussed in detail in relation to the initiation of autoxida-tion, one of the most important modes of formation of free radicals is by photoexcitation. The modes of formation can be generally classified as (A) bond-breaking reactions, (B) electron transfer reactions, and (C) reactions which in general form an electronically excited state of the absorbing molecule which produces atoms or free radicals in subsequent bimolecular collisions with other species present. 

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