photochemistry

Photochemistry is the branch of chemistry concerned with chemical reactions caused by absorption of visible light, ultraviolet, and infrared. The basic mechanism is absorption of a photon by an atom bringing it to a higher excited state, i.e., an electron is energized to take a higher orbit, which can change the likelihood of chemical reactions. For example, a reaction that requires some energy is more likely if that amount is available in atomic excitation due to absorption.