Theoretical study of electric moments, polarizabilities, and fine and hyperfine coupling constants of the B3Πg, C3Πu, A′5Σg+, and C″5Πu states of N2This article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.This paper is dedicated to Professors Ronald M. Lees and Colan Linton from the Department of Physics, University of New Brunswick.

Abstract

Several properties are calculated for the first time for the B3Πg, C3Πu, A′5Σg+, and C″5Πu states of N2, i.e., quadrupole (Θ) and hexadecapole (Φ) moments, static dipole polarizability (α), and hyperfine structure (hfs) data such as the electric field gradient (qii) and magnetic Frosch–Foley parameters (b, c, d). These quantities are evaluated with the density functional theory (DFT) method B3LYP/aug-cc-pVQZ. The variation with geometry is also considered for all parameters above. The B(σgπg) and C(σuπg) triplet Π states have similar values of the anisotropy P|2|(2) ∝ (Pxx − Pyy), with P = Θii, qii, or Tii (dipolar hfs tensor). The first-order spin-orbit coupling constant AΛ and the second-order electron-spin g-shift Δg⊥ are obtained with a 6-311+G(2d) basis and multireference configuration interaction (MRDCI) wave functions. Values of AΛ calculated for W3Δu and (B, C, C′, C″) Π states reproduce well the experimental data (C and C′ are two different minima of 13Πu). The variation of AΛ with R(N-N) is regular for all states studied, except for AΠ(13Πu), which changes abruptly between the C and C′ minima (from 38 to 2 cm−1). The Δg⊥ values — evaluated via sum over states expansions — are calculated for A′5Σg+ as well as A3Σu+ and B′3Σu−. The spin-rotation constant γΣ is derived via Curl’s equation γΣ = (−2B)Δg⊥. We find γΣ(A′) to be negative and to decrease steadily with vibrational excitation, in line with experimental observations. Both Δg⊥ and γΣ of A′5Σg+ are determined by the coupling of this weakly bound state with the strongly repulsive 15Πg state.