STUDIES OF CLUSTER ANIONS C(N)X(-) (X=N, P, AS, SB, BI) PRODUCED BY LASER-ABLATION

A series of cluster anions C(n)X(-) are produced from laser ablation of appropriate samples, where X is selected as a group-VB element. The recorded mass spectra of these cluster anions display a drastic even/odd alternation on ion intensities: For CnN-, only anions with odd n can be observed; For CnP- and CnAs-, cluster anions with even n are produced but with lower signal intensities; For CnSb-, the signal intensity of clusters does not show even/odd alternation; Finally, for CnBi-, the intensities of cluster anions with even n are higher than those with odd n. This parity effect can be attributed to the linear structure of the cluster anions, and the parity reversal of C(n)X(-) from CnN- to CnBi- can be explained from the electronegativity decreasing of the heteroatom X as it descends in the group. The Huckel model was applied to account the structural feature of these clusters.