Absorption Bunsen-Roscoe

Multiphoton processes are also undoubtedly involved in the photodegradation of polymers in intense laser fields, eg, using excimer lasers (13). Moreover, multiphoton excitation during pumping can become a significant loss factor in operation of dye lasers (26,27). The photochemically reactive species may or may not be capable of absorption of the individual photons which cooperate to produce multiphoton excitation, but must be capable of utilising a quantum of energy equal to that of the combined photons. Multiphoton excitation thus may be viewed as an exception to the Bunsen-Roscoe law. 

The physical meaning of the quantities a(A) and K X) can be stated thus the reciprocal of the Napierian coefficient of absorption a(A) corresponds to the thickness of the medium for which the incident intensity is divided by the base of the Napierian logarithm (i.e., e = 2.718281828...), while the reciprocal of the Bunsen-Roscoe coefficient of absorption K X) corresponds to the thickness of the medium for which the incident intensity is divided by ten. In most practical applications the decadic absorption coefficient is used, but the Napierian absorption coefficient is introduced more naturally in theoretical equations. 

This reaction was first thoroughly investigated by Bunsen and Roscoe in 1855 (Ostwald s Klassiker, 34 and 38) It had, of course, been the subject of earlier work, the most important conclusion of such work being the statement known as the Grotthus-Draper Absorption Law, vtz only those rays are effective which are absorbed Draper had also made the extremely interesting observation that chlonne which had been exposed to light had somewhat different properties from unexposed chlorine, in that the previously exposed chlonne reacted much more rapidly with... 

Bunsen and Roscoe thought they had shown that more light is absorbed by a mixture of hydrogen and chlorine than by an equal quantity of chlorine alone (they showed that the absorption by hydrogen is negligible). They called hv photochemical extinction,... 

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