Recommendation 2 of the 21st CCTF (2017)

Updates to the CIPM list of standard frequencies

The Consultative Committee for Time and Frequency (CCTF), at its 21st session in 2017,

considering that

• a common list of “Recommended values of standard frequencies for applications including the practical realization of the metre and secondary representations of the second” has been established,
• the CCL-CCTF Frequency Standards Working Group (WGFS) has reviewed several candidates for updating the list;

recommends that

the following transition frequencies shall be updated in the list of recommended values of standard frequencies:

• the unperturbed optical transition 5s^{2 1}S₀ – 5s5p ³P₀ of the ¹¹⁵In⁺ ion with a frequency of f_115In+ = 1 267 402 452 901 050 Hz and an estimated relative standard uncertainty of 1.6 × 10^–14;
• the unperturbed optical transition 6s^{2 1}S₀ – 6s6p ³P₀ of the ¹⁹⁹Hg neutral atom with a frequency of f_199Hg = 1 128 575 290 808 154.4 Hz and an estimated relative standard uncertainty of 5 × 10^–16;
  This radiation is now endorsed as a secondary representation of the second;
• the unperturbed optical transition 6s^{2 1}S₀ – 6s6p ³P₀ of the ¹⁷¹Yb neutral atom with a frequency of f_171Yb = 518 295 836 590 863.6 Hz and an estimated relative standard uncertainty of 5 × 10^–16 (this radiation is already endorsed by the CIPM as a secondary representation of the second);
• the unperturbed optical transition 5s ²S_1/2 – 4d ²D_5/2 of the ⁸⁸Sr⁺ ion with a frequency of f_88Sr+ = 444 779 044 095 486.5 Hz and an estimated relative standard uncertainty of 1.5 × 10^–15 (this radiation is already endorsed by the CIPM as a secondary representation of the second);
• the unperturbed optical transition 5s^{2 1}S₀ – 5s5p ³P₀ of the ⁸⁸Sr neutral atom with a frequency of f_88Sr = 429 228 066 418 007.0 Hz and an estimated relative standard uncertainty of 6 × 10⁻¹⁶;
• the unperturbed optical transition 5s^{2 1}S₀ – 5s5p ³P₀ of the ⁸⁷Sr neutral atom with a frequency of f_87Sr = 429 228 004 229 873.0 Hz and an estimated relative standard uncertainty of 4 × 10^–16 (this radiation is already endorsed by the CIPM as a secondary representation of the second);
• the unperturbed optical transition 4s ²S_1/2 – 3d ²D_5/2 of the ⁴⁰Ca⁺ ion with a frequency of f_40Ca+ = 411 042 129 776 399.8 Hz and an estimated relative standard uncertainty of 2.4 × 10^–15;
• the unperturbed ground-state hyperfine transition of ⁸⁷Rb with a frequency of f_87Rb = 6 834 682 610.904 312 6 Hz and an estimated relative standard uncertainty of 6 × 10⁻¹⁶ (this radiation is already endorsed by the CIPM as a secondary representation of the second);

and informs the CIPM accordingly.

DOI : 10.59161/CCTF2017REC2E