Chemiluminescence

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chemiluminescence

[‚kem·i‚lüm·ə′nes·əns]
(physical chemistry)
Emission of light as a result of a chemical reaction without an apparent change in temperature.

Chemiluminescence

 

luminescence associated with a chemical reaction. Either the reaction products or components excited as a result of energy transfer from the reaction products may emit the light. A special case of chemiluminescence is bioluminescence—for example, the glow of decaying wood or of certain insects and marine animals.

Chemiluminescence may accompany gase-phase, liquid-phase, or heterogeneous reactions. The emission spectrum may lie in the infrared, visible, or ultraviolet region. Chemiluminescence is observed in spontaneous reactions—that is, when reactants are mixed—and in reactions that occur, for example, during an electric discharge, during electrolysis (galvanoluminescence), or upon exposure to light or to ionizing radiation.

Chemiluminescence is an example of the direct conversion of chemical energy into luminous energy. The brightness of chemiluminescence is proportional to the reaction rate and to the efficiency of light production, that is, the number of photons emitted per reaction event. The efficiency of light production approaches 100 percent for the bioluminescence of certain fireflies and approaches 25 percent for reactions in which esters of oxalic acid are oxidized by hydrogen peroxide. In certain reactions (“bright” reactions), the efficiency is about 1 percent; in other cases, it is considerably lower. Therefore, highly sensitive photoelectric equipment is used to detect chemiluminescence, especially in slow reactions.

The study of chemiluminescence makes it possible to solve subtle theoretical problems regarding the elementary event of chemical conversion, the redistribution of energy in reaction products, and the structure of molecules. In addition, reaction rates or the concentrations of substances can be measured (see). Reactions characterized by intense chemiluminescence are used in chemiluminescent light sources, which are activated by the mixing of reactants and yield luminous fluxes of —0.1 lumen per milliliter of solution. Chemiluminescense is the basis for the operation of chemical lasers.

REFERENCES

Vasil’ev, R. F. “Mekhanizmy vozbuzhdeniia khemiliuminestsentsii.” Uspekhi khimii, 1970, vol. 39, issue 6, p. 1130.
Khemiliuminestsentnye metody issledovaniia medlennykh khimicheskikhprotsessov. Moscow, 1966.
Chemiluminescence and Bioluminescence. New York-London, 1973.

R. F. VASILEV