Hyperfine structure measurement of theBe 2 s ground state by optical pumping.

ThermalBe ( I=3/2) ions are polarized by direct optical pumping in He buffer gas. Observation of ⩼gDF=± 1 transitions yields for the hyperfine splitting frequency v(Be, 1 s 2 s S)=1250018(5) kHz. The result is discussed with regard to predictions of recent theoretical calculations and of the Fermi-Segré formula for the ground state hfs of the Li isoelectronic sequence. [ABSTRACT FROM AUTHOR]