The term systems of Be I converging to the Be II 2s limit

Abstract

In previous analyses of the Be I spectrum it has been assumed that the quantum defects mu ( epsilon ) can be fitted to low-order polynomials in the energy variable epsilon . Norcross and Seaton (1976) find the theoretical quantum defects, mu (theor mod epsilon ), for Be I 2snl levels are perturbed by states Be I 2pn'l' and, in consequence, cannot be fitted accurately to low-order polynomials. A new analysis of the Be I spectrum is made using calculated quantum defects mu (calc mod epsilon )= mu (theor mod epsilon )+ Delta mu (calc mod epsilon ) where the small correction Delta mu is assumed to be a linear or quadratic function, and where the parameters in Delta mu and the series limit Tinfinity are adjusted to give a least-squares fit to the experimental term values of Johansson (1974). A revised value (Tinfinity =75192.5+or-0.1 cm-1) of the limit is obtained and formulae are given for the accurate calculation of term values in the series 1S, 3S, 1P0, 3P0, 1D, 3D, 1F0 and 3F0. With the revised value of Tinfinity the experimental quantum defects for the 2sns 1S series show clearly the perturbation produced by the resonance state 2p2 1S above the Be II 2s limit.