Optical Pumping and Chemical Reactions

Abstract

Optical pumping in this paper refers to the orientation of the angular momenta of atoms and molecules by light. The phenomenon of spin exchange raises the possibility of the use of a gas of pumped atoms as a highly sensitive detector of free radicals. It is shown, however, that a suitable buffer gas may not have atoms of high atomic number, and may not be polar or aromatic and must be extraordinarily inert chemically. Examples are He, Ne, Ar, H₂, N₂, CH₄, C₂H₆, C₂H₄, and—for a short time—CO. These highly stable molecules decompose into radicals at ordinary temperature only under irradiation with vacuum ultraviolet photons or with particles. Optically pumped gases may be useful, therefore, in studying the reactions involved in vacuum uv photolyses of simple hydrocarbons.