Two-colour three photon resonance excitation spectra of lithium

Abstract

New observations of Rydberg states of atomic lithium excited by the two-colour three photon resonance ionization technique in conjunction with a space charge limited thermionic diode ion detector are reported. The odd parity Rydberg series 2s 2S1/2 to h omega 2P 2P1/2,3/2 to 2h omega nf2F5/2,7/2 have been detected for the first time for n=13 to 48, only 50 cm-1 from the ionization limit. By applying the Rydberg formula to the term energies, the ionization potential of lithium is found to be 43487.42+or-0.08 cm-1.