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

Abstract

We have measured the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ $2^{3}P-3^{3}D$ (5875 Å) and $2^{1}P-3^{1}D$ (6678 Å) lines by Doppler-free intermodulated fluorescence spectroscopy, and also the spin-forbidden $2^3{P}_{1,2}-3^1{D}_2$ (5874 Å) and $2^1{P}_1-3^3{D}_2$ (6679 Å) 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 $\sigma (2^3{P}_0-3^3{D}_1)=17013.762\mathrm{}08\left(9\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\sigma (2^3{P}_1-3^3{D}_2)=17014.705\mathrm{}78\left(9\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\sigma (2^3{P}_1-3^1{D}_2)=17018.123\mathrm{}8\left(4\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\sigma (2^1{P}_1-3^3{D}_2)=14\mathrm{}966.65204\left(10\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $\sigma (2^1{P}_1-3^1{D}_2)=14\mathrm{}970.06984\left(10\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The $2^{3}P-3\mathrm{}{}_{}{}^3{}_{}{}^{}D$ results are compared with two other recent determinations. A value of 1325.4(2.0) MHz obtained for the

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