Hyperfine structure in the two lowest electronic states of PrO by molecular-beam laser-rf double resonance

Abstract

The hyperfine structure (hfs) splittings in the electronic ground state ( Ω = 3.5 , v = 0) and the first excited electronic level (Energy = 220 cm −1, Ω = 4.5 , v = 0) of 141PrO have been measured over a broad range of J-values to a precision of about ±3 kHz. No perturbations are observed. The levels are represented as states of Pr(III) 4 f 26 s in an axial electric field, and the hyperfine structure resulting from the combined hfs and rotational Hamiltonians is worked out. The contribution due to the interaction between the two states of different Ω is found to be important. A single least-squares fit is made of the resulting theoretical expressions to the 166 radiofrequency (rf) measurements in the two states. Efforts are made to identify the contributions analogous to the conventional terms involving b, c, and eqQ. The perturbations in the optical spectra (of systems XVII and of the band at 6100 Å) are found to be in the common upper level (as previously reported), as is the Λ-doubling. The hyperfine structure of the upper state is determined to a precision of a few Mhz.