The optimized geometry of PCCP(X (1)Sigma(g)(+)) was calculated at a number
of levels of theory, yielding a best D-infinity h geometry at the QCISD/6-
311G(2d) level with RP-C = 1.56 Angstrom and RC-C = 1.37 Angstrom; harmonic
vibrational frequencies were also calculated. The four lowest cationic sta
tes were studied, allowing the lowest four ionization energies to be obtain
ed. At the G2 level of theory, the first adiabatic ionization energy was ca
lculated to be 9.5 eV. The ordering of the four lowest photoelectron bands
is found to be different to NCCN. The adiabatic electron affinity of PCCP i
s calculated at the G2 level to be 1.1 eV. Finally, the approximate positio
ns of the lowest singlet excited electronic states of the neutral are compu
ted.