We report on a precision measurement of the ${\left(5p\right)}^{5}6p{[1/2]}_0\leftarrow {\left(5p\right)}^6{}^{1}S_0$ transition wave number of Xe by Doppler-free two-photon spectroscopy using near-Fourier-transform-limited long pulses of UV-laser radiation. The measurements led to absolute uncertainties of 750 kHz in the two-photon transition wave numbers for the five dominant isotopes of Xe, e.g., 80 118.982 918(27) ${\mathrm{cm}}^{-1}$ for ${}^{136}\mathrm{Xe}$. These values were combined with other precision measurements in Xe to resolve an $\sim 1\text{−}\mathrm{GHz}$ discrepancy between the ionization energy of Xe obtained in recent measurements from the $\left(6s\right){[3/2]}_2$ metastable state [Herburger et al., Phys. Rev. A 109, 032816 (2024)] and the ionization energy listed in the NIST atomic database. The analysis indicates that the natural-abundance-weighted ionization energy of Xe should be revised by $-0.023{\mathrm{cm}}^{-1}$ to 97 833.7641(20) ${\mathrm{cm}}^{-1}$. Large fluctuations in the UV-laser pulse intensities were exploited to characterize intensity-dependent shifts of the observed two-photon transition frequencies. Shifts of up to $-20\mathrm{MHz}$ were observed and attributed to frequency shifts arising from chirps in the amplification and up-conversion of the laser radiation rather than to the ac-Stark effect.

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• Electronic excitation & ionization
• Atomic Properties
• Optical spectroscopy
• Photoexcitation
• Photoionization