Lasers and chemical change is the study of radiation and molecules in dis equilibrium. The distinguishing feature of such systems is the extreme de parture from thermal equilibrium: the radiation is usually confined to a narrow frequency range, is well coll imated, and is far brighter than black body radiation; the chemical composition and also the distribution of mole cules over their different energy states are often markedly displaced from that expected at equilibrium. Such systems can be used as a source of laser radiation and, reversedly, lasers can rapidly and selectively displace mole...