Negative ion photoelectron spectroscopy of P₂N₃^-: electron affinity and electronic structures of P₂N₃˙

We report here a negative ion photoelectron spectroscopy (NIPES) and ab initio study of the recently synthesized planar aromatic inorganic ion P₂N₃^-, to investigate the electronic structures of P₂N₃^- and its neutral P₂N₃˙ radical. The adiabatic detachment energy of P₂N₃^- (electron affinity of P₂N₃˙) was determined to be 3.765 ± 0.010 eV, indicating high stability for the P₂N₃^- anion. Ab initio electronic structure calculations reveal the existence of five, low-lying, electronic states in the neutral P₂N₃˙ radical. Calculation of the Franck-Condon factors (FCFs) for each anion-to-neutral electronic transition and comparison of the resulting simulated NIPE spectrum with the vibrational structure in the observed spectrum allows the first four excited states of P₂N₃˙ to be determined to lie 6.2, 6.7, 11.5, and 22.8 kcal mol^-1 above the ground state of the radical, which is found to be a 6π-electron, ²A₁, σ state.