Recommendation 1 of the 19th CCTF (2012)

Updates to the list of standard frequencies

The Consultative Committee for Time and Frequency (CCTF),

considering that

• 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 (FSWG) has reviewed several candidates for inclusion into the list,

recommends

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

• the unperturbed optical transition 3s^{2 1}S₀ – 3s3p ³P₀ of the ²⁷Al⁺ ion with a frequency of f_27Al+ = 1 121 015 393 207 857.3 Hz and an estimated relative standard uncertainty of 1.9 × 10⁻¹⁵.
  This radiation is recommended to be endorsed by the CIPM as a secondary representation of the second;
• the unperturbed optical transition 5d¹⁰6s ²S_1/2 – 5d ⁹6s^{2 2}D_5/2 of the ¹⁹⁹Hg⁺ ion with a frequency of f_199Hg+ = 1 064 721 609 899 145.3 Hz and an estimated relative standard uncertainty of 1.9 × 10⁻¹⁵ (this radiation is already endorsed by the CIPM as a secondary 
  representation of the second);
• the unperturbed optical transition 6s^{2 1}S₀ – 6s6p ³P₀ of the ¹⁹⁹Hg neutral atom with a frequency of f_199Hg = 1 128 575 290 808 162 Hz and an estimated relative standard uncertainty of 1.7 × 10⁻¹⁴;
• the unperturbed optical transition 6s ²S_1/2 – 4f ¹³6s^{2 2}F_7/2 of the ¹⁷¹Yb⁺ ion with a frequency of f_171Yb+ (octupole) = 642 121 496 772 645.6 Hz and an estimated relative standard uncertainty of 1.3 × 10⁻¹⁵.
  This radiation is recommended to be endorsed by the CIPM as a secondary representation of the second;
• the unperturbed optical transition 6s ²S_1/2 (F = 0, m_F = 0) – 5d ²D_3/2 (F = 2, m_F = 0) of the ¹⁷¹Yb⁺ ion with a frequency of f_171Yb+ (quadrupole) = 688 358 979 309 307.1 Hz and an estimated relative standard uncertainty of 3 × 10⁻¹⁵ (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+ = 444 779 044 095 485.3 Hz and an estimated relative standard uncertainty of 4.0 × 10⁻¹⁵ (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+ = 411 042 129 776 395 Hz and an estimated relative standard uncertainty of 1.5 × 10⁻¹⁴;
• the unperturbed optical transition 1S – 2S of the ¹H neutral atom with a frequency of f_1H = 1 233 030 706 593 518 Hz and an estimated relative standard uncertainty of 1.2 × 10⁻¹⁴.
  Note: This frequency corresponds to half of the energy difference between the 1S and 2S states;
• the unperturbed optical transition 5s^{2 1}S₀ – 5s5p ³P₀ of the ⁸⁷Sr neutral atom with a frequency of f_87Sr = 429 228 004 229 873.4 Hz and an estimated relative standard uncertainty of 1 × 10⁻¹⁵ (this radiation is already endorsed by the CIPM 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 = 518 295 836 590 865.0 Hz and an estimated relative standard uncertainty of 2.7 × 10⁻¹⁵.
  This radiation is recommended to be endorsed by the CIPM as a secondary representation of the second;
• the unperturbed ground-state hyperfine transition of ⁸⁷Rb with a frequency of f_87Rb = 6 834 682 610.904 312 Hz and an estimated relative standard uncertainty of 1.3 × 10⁻¹⁵ (this radiation is already endorsed by the CIPM as a secondary representation of the second).

Note: The value of the standard uncertainty is assumed to correspond to a confidence level of 68 %. However, given the very limited number of available data there is a possibility that in hindsight this might not prove to be exact.

and asks the CIPM for approval.

DOI : 10.59161/CCTF2012REC1E