Accurate wave-number measurements for theHe4i1s2p−1s3dtransitions and comparisons of several term separations with theory

Abstract

We have measured the /sup 4/He 2/sup 3/P-3/sup 3/D (5875 A) and 2/sup 1/P-3/sup 1/D (6678 A) lines by Doppler-free intermodulated fluorescence spectroscopy, and also the spin-forbidden 2/sup 3/P/sub 1,2/-3/sup 1/D/sub 2/ (5874 A) and 2/sup 1/P/sub 1/-3/sup 3/D/sub 2/ (6679 A) lines as observed in Doppler-limited fluorescence spectra. The positive column of a low-pressure discharge was the source of the excited He atoms. The wave number of the tunable dye laser inducing the fluorescence was measured relative to an iodine-stabilized He-Ne laser by photographic Fabry-Perot interferometry. The results are sigma(2/sup 3/P/sub 0/-3/sup 3/D/sub 1/) = 17 013.762 08(9) cm/sup -1/, sigma(2/sup 3/P/sub 1/-3/sup 3/D/sub 2/) = 17 014.705 78(9) cm/sup -1/, sigma(2/sup 3/P/sub 1/-3/sup 1/D/sub 2/) = 17 018.123 8(4) cm/sup -1/, sigma(2/sup 1/P/sub 1/-3/sup 3/D/sub 2/) p = 14 966.652 04(10) cm/sup -1/, and sigma(2/sup 1/P/sub 1/-3/sup 1/D/sub 2/) = 14 970.069 84(10) cm/sup -1/. The 2/sup 3/P-3 /sup 3/D results are compared with two other recent determinations. A value of 1325.4(2.0) MHz obtained for the 3/sup 3/D/sub 1/-3/sup 3/D/sub 2/ interval by combination of our results with the accurately known 2/sup 3/P/sub 0/-2/sup 3/P/sub 1/ interval is consistent with several previous measurements. The measurements of the spin-forbiddenmore » lines give a more accurate connection between the low triplet and singlet terms of this spectrum. We have reevaluated several term separations (directly from our measurements or by combining them with other recent results) for comparison with available calculations. The 2/sup 3/S-2/sup 3/P separation in combination with previous calculations gives an experimental value of -0.177 6(5) cm/sup -1/ for the Lamb-shift contribution to this separation, as compared with Ermolaev's theoretical value of -0.173 cm/sup -1/.« less