This law is also known as the photochemical equivalence law or also photo equivalence law. Between 1908 and 1913, Johannes Stark and the physicist, Albert Einstein independently formulated the Stark Einstein law.
The basic crux of the law states that each and every absorbed photon will bring forward a foremost chemical reaction or a physical reaction. The Stark Einstein law states that- for a reaction of a substance, per individual mole of the substance reacting, an equivalent amount of the mole of the quanta of the light gets absorbed.
One unit of radiation is basically termed as photon since the photon is basically a quantum of radiation. Hence the photon is a single unit of the electromagnetic radiation that is deemed equal to the Plank’s constant multiplied by the light’s frequency.
INTRODUCTION TO PHOTOCHEMICAL PROCESSES
The photochemical processes in the realm of photoelectrochemistry are the processes that involve the transmission of the light in other forms of energy. These processes apply to various fields like the sensitized solar cells, photochemistry, luminescence, optically pumped lasers and even photochromism.
The two basic laws of photochemistry are the Grotthuss-Draper Law and the Start-Einstein law. Grotthuss Draper law was given independently in 1817 by Theodor Grotthus and in 1842 by John William Draper.
The Grotthuss Draper law is also known as the basic principle of the photochemical activation which states that only the light which has been absorbed by the system can help in bringing forward the photochemical change.
APPLICATIONS OF THE STARK EINSTEIN LAW
The conventional photochemical processes which involve using the light sources with moderate to normal intensities, the photochemical equivalence law is restricted to them.
Biphotonic processes occur due to the high-intensity light sources like the ones used in laser experiments and in flash photolysis. Biphotonic processes are the processes involving the absorption of two photons of light by a molecule of a substance.
The Stark Einstein law or the photochemical equivalence law can be applied to the reaction which is induced by light which is also known as the primary process. This means the absorption and fluorescence.
The primary process in the photochemical reactions is mostly followed by the secondary photochemical processes. The secondary photochemical processes usually involve the regular interactions that take place between the reactants and there is no need of the light absorption.
Owing to this reason, the secondary photochemical reactions do not obey the relationship standards set by the reactant relationship of one-quantum one molecule.