Ultrahigh-resolution (1+1) photoionization spectroscopy of Kr I: Hyperfine structures, isotope shifts, and lifetimes for the n=5,6,7 4p5ns Rydberg levels.

Abstract

High-resolution measurements of the hyperfine structures and isotope shifts are reported for Kr i n=5,6,7 4${p}^{5}$ns Rydberg levels, obtained using an extreme-ultraviolet laser with a bandwidth of 210 MHz in a resonant two-photon-ionization scheme. Use of known ${\mathrm{I}}_{2}$ frequencies yields an improved absolute calibration of the Kr energy levels by more than one order of magnitude. The nuclear quadrupole hyperfine structure indicates that the 4${p}^{5}$6s and 4${p}^{5}$7s states are described by a pure jj-coupling scheme, whereas the 4${p}^{5}$5s states depart from a pure jj-coupling scheme by 0.37(6)%. The magnetic hyperfine structure shows that the 4${p}^{5}$ns states are mixed with 4${p}^{5}$n'd states. The isotope shifts can be described as pure mass effects within the precision of our experiment. For the 4${p}^{5}$6s and 4${p}^{5}$7s states, lifetimes were determined that differ markedly from theoretical literature values.