Dye laser study of the np 2P [formula omitted] Rydberg series in neutral gallium and indium atoms

Abstract

We investigated the np 2P 1 2 , 3 2 Rydberg series in indium and gallium. The high levels were populated in an atomic beam apparatus using stepwise excitation with two pulsed dye lasers. The series turn out to be unperturbed and the level values are described with high precision by extended Rydberg-Ritz formulae. From the accurate level values we determined the ionization limit of indium at 46 670.106±0.006 cm -1, and the ionization limit of gallium at 48 387.634±0.010 cm -1. The result for indium is in perfect agreement with earlier values derived from other Rydberg series. The fine structure splitting of the Rydberg states in gallium was resolved for the first time. The splitting is proportional to n ∗-3 over the range observed, just as in indium. Anomalies found for the fine structure intensity ratio in the transitions of both indium and gallium are discussed. From the measurements in gallium we have derived isotope shifts relative to the ionization limit for the 5s 2S 1 2 state, 7±4 mK, and the 4p 2P 1 2 and 2P 3 2 levels, 6±4 mK (1 mK is 0.001 cm -1).