Laser-optogalvanic studies of the 4p5 ns and nd autoionizing resonances in krypton

We report new measurements of the odd-parity autoionizing resonances in krypton using resonant two-photon excitation from the 4p(5)5s[3/2](2) metastable level in a mild DC discharge and an optogalvanic detection technique. We have observed the 4p(5)ns [1/2](0,1), 4p(5)nd [3/2](2) and 4p(5)nd [5/2](2,3) autoionizing resonances excited from three intermediate levels 4p(5)5p' [1/2](1), 4p(5)5p' [3/2](1) and 4p(5)5p' [3/2](2). The spectra are notable for the absence of the broad autoionizing 4p(5)nd [3/2](1) series which dominates in the photo-absorption spectrum from the ground state. The prominent transitions follow Delta K = Delta J = Delta l selection rules of the JK-coupling scheme. We report nearly 100 new energy levels in krypton besides the quantum defects and the reduced widths Gamma(r) = Gamma(v)(3) of the nd' [3/2](2), nd' [5/2](2) and nd' [5/2](3) Rydberg states.