Study of the ns²S and nd²D Rydberg series in aluminium

Abstract

The authors investigated the 3s2ns 2S Rydberg series and salient features of the 3s2nd 2D3/2, 5/2, series in free aluminium atoms. The high 2D and 2S levels were populated by stepwise excitation using 4s 2S1/2 as the intermediate state. They determined the position of the series members accurately from the normally forbidden 4s 2S-ns 2S and 4s 2S-nd 2D transitions (37<or=n<or=55) in a weak electric field. The 2S series is not perturbed; its quantum defect is 1.729(2). The 2D series is strongly perturbed by interaction with the 2D term of the 3s3p2 configuration and with other configurations. A new value for the ionisation limit is derived: 48278.372(1) cm-1. The fine-structure splitting of the high 2D levels has been estimated for the first time. The splitting is very large, due to a perturbation of the series. The authors' results are compared with other aluminium data as well as with data from the elements gallium and indium.