Photochemical monophotonic

The quantum yield of photochemical processes can vary from a low fractional value to over a million (Section 1.2). High quantum yields are due to secondary processes. An initially excited molecule may start a chain reaction and give rise to a great number of product molecules before the chain is finally terminated. For nonchain reactions, the quantum yields for various competitive photophysical and photochemical processes must add up to unity for a monophotonic process if the reaction occurs from the singlet state only ... 

Monophotonic photochemical reactions are those where each absorbed quantum excites one molecule which then reacts. Rates are usually directly proportional to the light intensity. Where secondary reactions are set up, however, the proportionality changes, depending on the chain termination processes. If chain intermediates are terminated by unimolecular reactions,... 

Primary photoprocesses and photochemical behaviour of proflavin have been investigated in aqueous and anionic micellar solutions. Micellar environments affect the pK of the singlet and triplet excited states owing to differences in surface and bulk pH. The photoredox behaviour is due to monophotonic photoionization and triplet-triplet annihilation gives rise to oxidized and reduced proflavin radicals in water, whereas biphotonic photoionization occurs in micelles. Photoredox processes have also been studied in Zn-tetraphenylporphyrin-methylviologen surfactant assemblies. 

The quantum efficiency of secondary photochemical processes varies from fractional value to several millions. This is due to the fact that initially excited molecule starts a chain of excitation (like photo degradation of ozone by chloro-floro hydrocarbons). Those reactions which are monophotonic occur from singlet excited state... 

Intensity of light at a point is defined as the number of photons passing through the point per second. Therefore intensity is directly proportional to the number of photons. Primary photochemical reactions are Monophotonic photochemical reactions where each absorbed quanta excites one molecule which then reacts. That s why the rate of primary photoreactions is usually directly proportional to the light intensity [Rate c /]. But in case of secondary photochemical reactions [which are initiated by species formed by primary photochemical reactions], the proportionality depends on the ... 

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