Observation of the highly excited states of Lanthanum

The highly excited states of Lanthanum are studied by means of laser resonance ionization time-of-flight spectrometer. Based an the two-step laser resonance excitation with intermediate state 5d(2)(F-3)6p D-2(5/2)0. three new Rydberg state (RS) series (5d(2)(a(3)F(2))ns, 5d(2)(a(3)F(3))nd and 5d(2)(a(1)D(2))ns) and a number of autoionizing states (AIS) are obtained. Theoretical calculation lends the quantum defects of ns and nd series to the value delta s=4.35 and delta d=2.80 respectively, which are very close to the experimental results. The Rydberg state series 5d(2)(a(3)F(2))ns gives the first ionization limit to be 44979.8 +/- 0.3 cm(-1), which is an order more accurate than ever.