MILLIMETER WAVE SPECTROSCOPY AND MQDT CALCULATIONS OF HIGH RYDBERG STATES OF KRYPTON

Abstract

A phase-stabilised backward wave oscillator (BWO) in the 260--380 GHz range was combined with a VUV laser system to record high-resolution spectra of high-$n$ Rydberg states of krypton. Krypton atoms were excited into $n$p ($n$=58,60) Rydberg states via the 4d[1/2] ($J=1$) state using VUV and visible laser photons. Millimeter wave transitions between $n$p and $n$s or $n$d Rydberg states were detected by pulsed field-ionization, at sub-MHz resolution and with mass selection. Using this excitation scheme, very accurate relative energies of fine and hyperfine structure levels of $(n+2)$s and $n$d ($n$=68--74) Rydberg states of $^{84}$Kr and $^{83}$Kr were obtained. In this region, s-d interactions are observable for $^{83}$Kr due to the hyperfine interaction. A multichannel quantum defect theory (MQDT) treatment of the hyperfine structure% }, \emph{Phys.\ Rev.\ A}, \textbf{68}, 032510 (2003).} was used to analyze the millimeter wave data in combination with recent high-resolution VUV laser data$^a$ and the available data from the literature; improved MQDT parameters and hyperfine structure data of the $^2$P ground electronic state of $^{83}$Kr$^+$ were obtained.