The mercury single-ion optical clock and a test of the stability of the fundamental constants

Summary form only given. Results of the measurements which compare the frequency ν/sub Hg/ of the /sup 199/Hg/sup +2/ S/sub 1/2/ (F=0) - /sup 2/D/sub 1/2/ (F=2, m/sub F/=0) optical transition to the SI second as realized at NIST are reported. Since the NIST time scale is calibrated with a cesium fountain primary frequency standard, the ratio of ν/sub Hg/ ( ≈ 10/sup 15/ Hz) to the cesium ground-state hyperfine splitting ν/sub Cs/ (≈ 9.2 GHz) is measured. These measurements show better reproducibility than 10 Hz at ν/sub Hg/, and constrain any possible variation of the ratio ν/sub Hg/ /ν/sub Cs/ to ± 7·10/sup -15/ yr/sup -1/.