Recommendation 2 of the 17th CCTF (2006)

Concerning secondary representations of the second

The Consultative Committee for Time and Frequency (CCTF),

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” shall be established,
• the CCL/CCTF Joint Working Group (JWG) on the Mise en Pratique of the Definition of the Metre and the Secondary Representations of the Second in its meeting at the BIPM in September 2005 discussed possible candidates to be included in this list for secondary representations of the second,
• the CCL/CCTF JWG reviewed and updated the values for the Hg ion, Sr ion, Yb ion, and the Sr neutral atom transition frequencies in its session in September 2006,
• the CCTF in its Recommendation CCTF 1 (2004) already recommended the unperturbed ground-state hyperfine quantum transition frequency of 87Rb as a secondary representation of the second;

recommends that the following transition frequencies shall be used as secondary representations of the second and be included into the new list of “Recommended values of standard frequencies for applications including the practical realization of the metre and secondary representations of the second”:

• the unperturbed ground-state hyperfine quantum transition of ⁸⁷Rb with a frequency of f_87Rb = 6 834 682 610.904 324 Hz and an estimated relative standard uncertainty of 3 × 10⁻¹⁵,
• the unperturbed optical 5s ²S_1/2 – 4d ²D_5/2 transition of the ⁸⁸Sr⁺ ion with a frequency of f_88Sr+ = 444 779 044 095 484 Hz and a relative uncertainty of >7 × 10⁻¹⁵,
• the unperturbed optical 5d¹⁰ 6s ²S_1/2 (F = 0) – 5d⁹ 6s^{2 2}D_5/2 (F = 2) transition of the ¹⁹⁹Hg⁺ ion with a frequency of f_199Hg+ = 1 064 721 609 899 145 Hz and a relative standard uncertainty of 3 × 10⁻¹⁵,
• the unperturbed optical 6s ²S_1/2 (FF = 0) – 5d ²D_3/2 (F = 2) transition of the ¹⁷¹Yb⁺ ion with a frequency of f_171Yb+ = 688 358 979 309 308 Hz and a relative standard uncertainty of 9 × 10⁻¹⁵,
• the unperturbed optical transition 5s^{2 1}S₀ – 5s 5p ³P₀ of the ⁸⁷Sr neutral atom with a frequency of f_87Sr = 429 228 004 229 877 Hz and a relative standard uncertainty of 1.5 × 10⁻¹⁴.

DOI : 10.59161/CCTF2006REC2E