Abstract: Negative carbon cluster ions were generated on a conventionally made laser probe time-of-flight mass spectrometer. The mass spectra showed an even/odd alternation of the cluster ion intensities with cluster size up to 12, indicating a chain configuration. For cluster anions larger than 12, the ions containing 4m+1 carbon atoms have higher concentrations in the cluster anion beam, and a cyclic model can explain the observation very well. We therefore conclude that the chain-ring transi-tion occurs at n=12.