Studies of cluster anions C n X? (X=N, P, As, Sb, Bi) produced by laser ablation

Abstract

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 C n N−, only anions with oddn can be observed; For C n P− and C n As−, cluster anions with evenn are produced but with lower signal intensities; For C n Sb−, the signal intensity of clusters does not show even/odd alternation; Finally, for C n Bi−, the intensities of cluster anions with evenn are higher than those with oddn. This parity effect can be attributed to the linear structure of the cluster anions, and the parity reversal of C n X− from C n N− to C n Bi− 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.