ISOTOPE SHIFT IN THE NEON GROUND-STATE BY EXTREME-ULTRAVIOLET LASER SPECTROSCOPY AT 74 NM

Narrow-band extreme-ultraviolet (xuv) radiation in the range 73.5-75.5 nm has been produced in Xe by generating the third harmonic of light from a frequency-doubled, pulsed blue-dye laser. In a one-xuv-photon plus one-uv-photon ionization process both 2p(6)-2p(5)3s[3/2](1) and 2p(6)-2p(5)3s'[1/2](1) transitions in Ne-20 and Ne-22 were observed. Frequencies were calibrated using a tellurium absorption spectrum of the fundamental blue light. Frequencies of 134459.33(5) cm(-1) for the 2p(6)-2p(5)3s[3/2](1) and 135888.73(5) cm(-1) for the 2p(6)-2p(5)3s'[1/2](1) transition in Ne-20 are obtained. In both transitions the isotope shift (Ne-20-Ne-22) was measured. The values are -0.014(3) cm(-1) and +0.003(3) cm(-1), respectively. Combined with existing values for the 3s[3/2](1) and 3s'[1/2](1) level shifts, a value for the ground-state specific mass shift of 9.54(15) GHz is deduced, in good agreement with a theoretical value of 10.1 GHz.