Measurements are reported for an improved value of the **2**0**3Hg minus **1**9**8Hg isotope shift in the 2537 A **3P//1 minus **1S//0 line of mercury by means of emission spectroscopy with mass-separated samples and by absorption spectroscopy with unenriched pile-produced isotope. The new value of the isotope shift is IS(203 minus 198) equals 0. 392 plus or minus 0. 006 cm** minus **1. **2**0**3Hg lies at the lower-wavenumber.
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