On the lowest-lying states and electronic structure of the ScN+ and ScP+ isovalent ions

The primary purpose of this investigation is to compare the electronic stru cture and stability of the ScN+ and ScP+ isovalent systems. These cations h ave quasi-degenerate electronic states requiring extensive configuration in teraction. CIPSI (Configuration Interaction by Perturbation of a multiconfi guration wavefunction Selected Iterative) wavefunction have been used to de termine the lowest electronic states of both ions. Only two states are fair ly bound, namely (2)Sigma(+) and (2)Pi. Contrary to a previous theoretical study, the two isovalent species ScN+ and ScP+ are found similar with regar d to their lowest (2)Sigma(+) ground state and first (2)Pi excited state. T he magnitude of the (2)Sigma(+)-(2)Pi splitting in ScP+ was computed by sev eral ab initio methods: variation-perturbation configuration interaction (CIPSI), fourth-order Moller-Plesset perturbation theory (MP4), variational quadratic configuration interaction (QCISD(T)), in order to settle the (2)Sigma(+)-(2)Pi Ordering states. The effect of cor relation energy on the relative stability of these two states and the origi n of their small splitting have been investigated. The molecular spectrosco pic constants of both cations are reported and some differences are pointed out. (C) 1999 Elsevier Science B.V. All rights reserved.