Abstract: Aseries of carbon cluster anions with a phosphorus atom had been produced in theexperiment.Ab initio balculations at the HF/6-311^*.level were carried out on the cluster ionswith linear configuration.The calculated electronic structure, system energy and fragmenta-tion energies of six dissociation channels exhibit odd/even alternation which agrees very wellwith the experimental observations.According to the calculated results, HOMOof C_nP^- with odd n is full-filled bonding orbitals, so it is more stable than C_nP^- with even n, whoseHOMOis also doublet degenerated but it is half-filled non-bonding orbitals.The optimizedbond lengths of the cluster anions show that CusPbond of C_nP^- with odd n is triplet.Oncontrast, the bond of C_nP^- with even n is singlet, so it is easier to be broken.

Key words: Ab initio calculation, C_nP^-, Dissociation energy, Stability