Abstract: Molecules to be separated from a mixture of matter of a chemical component are excited in a manner known per se by narrow-band light sources, and a chemical reaction partner for reacting with these molecules is admixed while supplied with energy by electromagnetic radiation or heating, as an addition required for making chemical reactions possible. The mixture and the partner are physically separated while the mixture is being excited and while the partner is being supplied with the energy, the two then being mixed together to cause the reaction.