Isotope shift metrology in the deep-UV region has been performed for all bosonic isotopes of mercury with a zero nuclear spin, using the technique of frequency-comb referenced, wavelength-modulated, saturated absorption spectroscopy. The absolute center frequencies of the $6{\mathrm{s}}^2{{}^1\mathrm{S}}_0\to 6\mathrm{s}6\mathrm{p}{{}^3\mathrm{P}}_1$ transition have been measured with precision in the range of $2.5–5.9{10}^{-12}$ in temperature-stabilized Hg vapor samples with natural abundances. Frequency shifts in four isotope pairs have been determined with unprecedented accuracy, the global uncertainty being improved by a factor greater than 20 with respect to the best experimental data of the past literature. Our dataset, when combined with previous measurements on the 6s6p ${{}^3\mathrm{P}}_2\to 6\mathrm{s}7\mathrm{s}$ ${{}^3\mathrm{S}}_1$ transition at 546 nm, allows us to build a King plot that reveals a nonlinearity with a statistical significance of $4.6\sigma$.

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• Isotope shift
• Laser spectroscopy
• Atomic gases
• Laser techniques
• Precision measurements