AN AB-INITIO STUDY ON THE ELECTRONIC-STRUCTURE OF THE 3(2)SIGMA(-2(+)()(U), 3(2)SIGMA(+)(G) AND 4(2)SIGMA(+)(G) STATES OF N)

The electronic structure of the 3(2)Sigma(u)(+), 3(2)Sigma(g)(+) and 4 (2)Sigma(g)(+) states of N-2(+) are studied by using configuration int eraction calculations at and around the equilibrium internuclear dista nce R-e = 2.074 au of the N-2 ground state. The vertical excitation en ergies relative to the N-2(+) 1(2) Sigma(g)(+) ground state at R = 2.0 74 au are calculated to be 17.24 eV (3(2)Sigma(u)(+)), 17.95 eV (3(2)S igma(g)(+)) and 18.37 eV (4(2)Sigma(g)(+)). An avoided crossing is fou nd between the 3(2)Sigma(g)(+) and 4(2)Sigma(g)(+) potential energy cu rves in the Franck-Condon region of the N-2 ground state. This avoided crossing results from the mixing between valence-type and diffuse con figurations. The 3(2)Sigma(g)(+) state in R = 1.920-2.037 au and the 4 (2)Sigma(g)(+) state in R = 2.074-2.220 au correspond to the lowest di ffuse (2)Sigma(g)(+) state, whose diffuse character is attributed to t he N-2(+) 4 sigma(g) molecular orbital (MO). The characterization of t he 4 sigma(g) MO reveals its marked similarity with the H-2(+) 2 sigma (g) MO. From this similarity, it is inferred that the nature of the lo west diffuse (2)Sigma(g)(+) state is considered as the lowest Rydberg- type (2)Sigma(g)(+) state. The 3(2)Sigma(u)(+) state is inferred to ta ke on a Rydberg-type character of about 11% at R = 2.074 au. (C) 1998 Elsevier Science B.V. All rights reserved.