Recommendation 1 of the 13th CCL (2007)

Revision of the list of standard frequencies

Part a

The Consultative Committee for Length,

considering that:

• improved frequency values of molecules in the optical telecommunications region, already documented in the list of standard frequencies, have been determined by femtosecond comb-based frequency measurements;
• frequencies of molecules in the optical telecommunications region have been determined by femtosecond comb-based frequency measurements for the first time;
• frequencies of certain iodine gas-cell absorptions close to the 532 nm optical frequency standard have been determined by femtosecond comb-based frequency measurements for the first time;

proposes that the list of standard frequencies be revised to include the following:

• an updated list of frequency values for the ¹²C₂H₂ (ν₁ + v₃) band at 1.54 µm;
• the addition of frequency values for the ¹²C₂HD (2ν₁) band at 1.54 µm;
• the addition of frequency values for the hyperfine components of the P(142) 37-0, R(121) 35-0 and R(85) 33-0 iodine absorptions at 532 nm.

Part b

proposes that the CIPM adopt the following radiation values for addition to the list of standard frequencies:

• ¹²C₂HD, (2ν₁) band at 1.54 µm

Hyperfine components of the P(142) 37-0, R(121) 35-0 and R(85) 33-0 absorptions at 532 nm

• f_a1 [P(142) 37-0] - f_a10 [R(56) 32-0] = 20 123 511.4 (5.0) kHz

• f_a1 [R(121) 35-0] - f_a10 [R(56) 32-0] = 27 539 228.6 (5.0) kHz

• f_a1 [R(85) 33-0] - f_a10 [R(56) 32-0] = 46 496 559.1 (5.0) kHz

DOI : 10.59161/CCL2007REC1E