Rotational studies of the Gaydon-Herman (green) bands of N2

Abstract

The Gaydon-Herman green system of N2 has been studied under high resolution and rotational analyses made of the 0-0, 1-0, 2-1, 2-0 and 3-1 bands. It is shown that the transition involved is 3 Phi u-3 Delta g. The 3 Delta g state (which it is proposed to call G) shows essentially pure case b coupling and its fine structure can be interpreted in terms of spin-orbit and spin-spin interactions. The 3 Phi u state (called H) is inverted and close to case a at low J values. Its energy levels can be represented by the usual formulae for coupling intermediate between cases a and b to which a small correction must be added for spin-spin interaction and/or a singlet-triplet perturbation. Both states have relatively shallow potential curves and rather large equilibrium internuclear distances. From simple molecular orbital considerations it can be shown that both states arise by the simultaneous excitation of two valence-shell electrons, G 3 Delta g being derived from ...(1 pi u)2(3 sigma g)2(1 pi g)2 and H 3 Phi u from ...(1 pi u)3(3 sigma g)(1 pi g)2.