The<unk>  of a radiation-induced process is the number of times that a defined event  occurs per photon absorbed by the system. Thus, the<unk>  is a measure of the efficiency with which absorbed light produces some effect.
For example, in a chemical photodegradation process, when a molecule falls apart after absorbing a light<unk> , the<unk>  is the number of destroyed molecules divided by the number of photons absorbed by the system. Since not all photons are absorbed productively, the typical<unk>  will be less than 1.<unk> s greater than 1 are possible for photo-induced or radiation-induced chain reactions, in which a single photon may trigger a long chain of transformations. One example is the reaction of hydrogen with chlorine, in which a few hundred molecules of hydrochloric acid are typically formed per<unk>  of blue light absorbed.
In optical spectroscopy, the<unk>  is the probability that a given<unk>  state is formed from the system initially prepared in some other<unk>  state. For example, a singlet to triplet transition<unk>  is the fraction of molecules that, after being photoexcited into a singlet state, cross over to the triplet state. The fluorescence<unk>  is defined as the ratio of the number of photons emitted to the number of photons absorbed.
Quantum yield
Equation of state
Greenhouse effect
Extraction ratio
Reaction rate constant
Spin quantum number
Potential energy
Gibbs free energy