Laser-microwave spectroscopy of lithium ions: 23 S 1 hyperfine structure of7Li+

Abstract

The hyperfine structure (hfs) splittings of the metastable 1s2s3S1 state of7Li+ have been measured with combined laser optical pumping and microwave resonance. A lowenergy Li+ ion beam, optically excited by an intersecting laser beam, passed a waveguide where radio frequency transitions were induced. The resulting population transfer among the hfs levels of the3S1 was detected via the change in intensity of the fluorescence light from a second crossing region of laser light and ion beam located past the waveguide. The magnetic hfs constantA(7Li+, 1s2s3S1) was measured and compared with theory. A deviation of the two transition frequenciesν(F=3/2−F=5/2) andν(F=1/2−F=3/2) from the interval rule is due to a depression of theF=3/2 hfs sublevel, caused by mixing of the 23S1 and 21S0 states via hyperfine interaction. This shift was never observed so far in a two-electron spectrum, because of absence ofI>1/2 isotopes in He, the only two-electron atom investigated spectroscopically with high precision. The size of the shift is in fair agreement with a theoretical estimate.