In this work, the structures, vertical electron detachment energies and fragmentation energies of CnP- 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 sp 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 CnP- (n=4 to 7) clusters are slightly bent, and the bent C,P-with odd n is very floppy for bending motion. The contributions of the bending of the structures of CnP- 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 CnP- (n=1 to 7) in their ground states reveal that the CnP- 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 CnP- is weaker than that of CnN-. Therefore, the stability difference for CnP- between the odd n and even n is smaller than that for CnN-. This conclusion is also coincident with the experimental observation reported. (C) 1997 American Institute of Physics.