We report here the results of a combined experimental and computational study of the negative ion photoelectron spectroscopy (NIPES) of the recently synthesized, planar, aromatic, HCPN3- ion. The adiabatic electron detachment energy of HCPN3- (electron affinity of HCPN3 center dot) was measured to be 3.555 +/- 0.010 eV, a value that is intermediate between the electron detachment energies of the closely related (CH)(2)N-3(-) and P2N3- ions. High level electronic structure calculations and Franck-Condon factor (FCF) simulations reveal that transitions from the ground state of the anion to two nearly degenerate, low-lying, electronic states, of the neutral HCPN3 center dot radical are responsible for the congested peaks at low binding energies in the NIPE spectrum. The best fit of the simulated NIPE spectrum to the experimental spectrum indicates that the ground state of HCPN3 center dot is a 5 pi-electron (2)A '' pi radical state, with a 6 pi-electron, (2)A', sigma radical state being at most 1.0 kcal/mol higher in energy.