It is shown that the sequential implantation of 20–200 keV C+and N+ions into a KCl crystal gives rise to formation of the CN−molecular configuration. Detection of the CN−is by the characteristic luminescence spectrum induced when He+ions are incident on the implanted target, a technique which represents a directinsitudetermination of their presence. It is shown how the ion‐induced optical emission may be used to provide a routine relative measurement of the quantity of CN−present. We describe a phenomenological model of the formation process which leads to the conclusion that each incoming ion searches a volume of the target approximately 3.4×10−21cm3in extent and has a unit probability of combining with an atom of the other species lying in this region. This model explains why saturation of the CN−density occurs at a N+dose independent of the quantity of C+implanted previously.