Charge-transfer excitation processes in the Grimm lamp

The differences in electrical and spectral characteristics that occur when plane and hollow cathodes are used in a Grimm discharge lamp are reported briefly. For copper-argon systems, with either a plane or a hollow cathode, the 224.7-nm Cu II line is exceptionally intense, and it is argued that the upper level concerned is populated by charge-transfer excitation. The relevance of this hypothesis to the deeper understanding of the Grimm lamp discharge is discussed.