Spectroscopic properties of Al2P2, Al2P2+, and Al2P2- and comparison with their Ga and In analogues

Sixteen electronic states of Al2P2, three states of Al2P2+, and the ground state of Al2P2- are studied using the complete active-space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction (MRS DCI). The (1)A(g), B-2(1u), and B-2(1g) electronic states with rhombus equi librium structures were found to be the ground states of Al2P2, Al2P2+, and Al2P2-, respectively. Alternative structures such as T-shaped, linear, and trapezoidal structures were considered, but the equilibrium geometry of th e ground state was found to be the rhombus structure. Our computed results are compared with anion photoelectron spectroscopic studies of Neumark and co-workers. Comparison of electronic states of M2P2 (M = Al, Ga, and In) wa s made. It is shown that the electronic states of In2P2 exhibit anomalies d ue to relativistic effects.