Ab initio studies on the structures, vertical electron detachment energies, and stabilities of C_nP^- clusters

In this work, the structures, vertical electron detachment energies and fragmentation energies of C_nP^- clusters (n = 1 to 7) have been investigated by carrying out the geometry optimizations with MP2 method using 6-31G(d) augmented with a set of diffuse s p functions followed by the energy calculations at higher levels. It can be concluded from our calculated results that for the ground states the linear structures are stable only for C₂P^- and C₃P^-. Other C_nP^- (n = 4 to 7) clusters are slightly bent, and the bent C_nP^- with odd n is very floppy for bending motion. The contributions of the bending of the structures of C_nP^- with odd n to the stability can be ignored, and therefore these clusters could appear pseudolinear in experiment. The calculated vertical electron detachment and fragmentation energies of C_nP^- (n = 1 to 7) in their ground states reveal that the C_nP^- clusters with odd n are more stable than those with even n, which is consistent with the observed odd-even alternation in the TOF signal intensities. It has been also found that the odd-even alternation in fragmentation energies of C_nP^- is weaker than that of C_nN^-. Therefore, the stability difference for C_nP^- between the odd n and even n is smaller than that for C_nN^-. This conclusion is also coincident with the experimental observation reported.