Electronic states of Al3P2, Al2P3, and their ions

Complete active-space self-consistent field (CASSCF) method followed by multireference singles + doubles configuration interaction (MRSDCI) calculations that included up to 4 million configurations were carried out on the electronic states of Al3P2, Al2P3 and their anions and cations. Our computed results explain the recently reported anion photoelectron spectra of Al2P3- and Al3P2- by Neumark and co-workers.(1) We find that both the Al2P3- and Al2P3 species have D-3h undistorted trigonal bipyramidal structures consistent with the sharp and intense ground-state peak in the observed spectra. But the neutral Al3P2 cluster was found to be Jahn-Teller distorted in contrast to the Al3P2- anion, which has a D-3h undistorted trigonal bipyramidal structure, consistent with the observed extended vibrational progression of the X state of the spectra. Our computed electron affinities agree well with the onsets of the observed X peaks in both spectra. We assign the partially resolved vibrational structure in the observed spectra to the totally symmetric stretch mode than to symmetry lowering of Al2P3, which is found to be in a (2)A(2)" (D-3h) state and cannot undergo Jahn-Teller distortion. Seven electronic states of Al3P2 are computed, among which the (2)A(1)(C-2v) state is the ground state with a distorted trigonal bipyramid structure. The distorted(2)A(1) and B-2(1) (C-2v) states are identified as Jahn-Teller components of the Undistorted E-2' and E-2 " (D-3h) states, respectively. Properties of four electronic states of Al2P3, Al3P2+, and Al2P3+ are also reported. The ground states of both Al3P2+ and Al2P3+ are undistorted (3)A(2)' and (1)A(1)', respectively (D-3h symmetry). The atomization energy, adiabatic ionization potentials, dipole moments, and other properties for the electronic states of Al3P2 and Al2P3 are calculated and discussed. Comparisons are made with the Ga and In analogues of these species.