Dissociation energies for carbon cluster ions (C+2--15): A system where photodissociation is misleading

This letter reports a collision-induced dissociation study of the stabilities and fragmentation patterns for carbon cluster ions C+n (n = 2--15). For clusters of six or more atoms, the primary fragmentation channel is loss of C3 neutral. Fragmentation thresholds are analyzed to yield dissociation energies, which are found to be substantially higher than the upper limits estimated from photodissociation experiments of Geusic et al. [Z. Phys. D 3, 309 (1986)], but in good agreement with theoretical estimates. The stabilities oscillate strongly, with some evidence of a change in behavior as size increases above 9 atoms. This is the size where the most stable structure is believed to change from linear to cyclic. Photodissociation measurements were also done, and we find that the clusters dissociate efficiently at photon energies far below the CID thresholds. Possible reasons for the anomalous photodissociation results are discussed