Abstract
A two-step optical excitation, starting from a metastable level, has been used to populate Rydberg levels in a krypton atomic beam. The metastable level is populated in the beam 'oven' by means of a HF discharge and the Rydberg atoms are detected by the field ionisation method. Using two N2-pumped pulsed dye lasers, the Rydberg spectra have been obtained with a resolution better than 0.1 cm-1. The fine structure of the (4p5)2P3/2 nd sub-configuration has been resolved and the wavenumber of the corresponding transition has been measured with an absolute accuracy of 0.03 cm-1. The energies of 187 levels (n>or=24) belonging to seven different series, 4p5nd and 4p5ns, have been determined; 153 of these levels (J=2 and J=3) had never been observed before. The value of the first ionisation limit has been redetermined to be I=(112914.47+or-0.03) cm-1. The critical ionisation fields and the lifetimes of some of the Rydberg levels have also been measured. Significant deviations from the hydrogenic model laws been found in both cases.