Improved determinations ofnD2andnF2fine-structure intervals in neutral cesium

We have observed fine-structure intervals in Cs I using high-resolution Fourier spectroscopy. Improved values are reported for the $5,6{}_{}{}^2{}_{}{}^{}D$ and $4-9{}_{}{}^2{}_{}{}^{}F$ terms and are shown to be consistent with recent laser fluorescence measurements of the $10-17{}_{}{}^2{}_{}{}^{}F$ intervals. The results are compared with previous measurements. A three-term expansion in odd powers of $\frac{1}{n^{*}}$ is shown to describe all of the $4-17{}_{}{}^2{}_{}{}^{}F$ fine-structure intervals. The state of experimental and theoretical work on the doublet structure in the alkali metals is briefly reviewed.