Accurate energies ofnS,nP,nD,nF, andnGlevels of neutral cesium

Extensive measurements have been performed to determine the absolute energies of the n ${\mathrm{}}^2$ $S_{1/2}$ (n=8–31), n ${\mathrm{}}^2$ $P_{1/2}$ (n=6,9–80), n ${\mathrm{}}^2$ $D_{5/2}$ (n=5,7–36), n ${\mathrm{}}^2$ $F_{5/2}$ (n=6–65), and n ${\mathrm{}}^2$ $G_{7/2}$ (n=6–54) levels of Cs by using nonresonant and resonantly enhanced Doppler-free two-photon spectroscopy. The excitation mechanisms employed include resonantly enhanced dipole-quadrupole and quadrupole-quadrupole transitions. All energies were measured directly with respect to the 6 ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$ ground state. The laser wavelengths were measured by high-precision Fabry-Perot interferometry yielding an uncertainty of 0.0002 ${\mathrm{cm}}^{\mathrm{-}1}$ for most Cs levels. Ionization energies derived by fitting the modified Ritz formula to each of the five series observed coincide within 0.000 05 ${\mathrm{cm}}^{\mathrm{-}1}$. Taking account of possible systematic errors, the Cs ionization energy is 31 406.467 66(15) ${\mathrm{cm}}^{\mathrm{-}1}$.