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
![](/documents/20126/60632397/CCL13+Recommendation+1+Table+1.png/8c70d785-c645-d423-3ceb-3a7c339573bc?t=1632824226318)
Hyperfine components of the P(142) 37-0, R(121) 35-0 and R(85) 33-0 absorptions at 532 nm
- fa1 [P(142) 37-0] - fa10 [R(56) 32-0] = 20 123 511.4 (5.0) kHz
![](/documents/20126/60632397/CCL13+Recommendation+1+Table+2.png/57905b0d-70c4-4bed-117e-45a41867d315?t=1632824233554)
- fa1 [R(121) 35-0] - fa10 [R(56) 32-0] = 27 539 228.6 (5.0) kHz
![](/documents/20126/60632397/CCL13+Recommendation+1+Table+3.png/eef13c53-e936-e7fb-3083-c33d891a1eb4?t=1632824236985)
- fa1 [R(85) 33-0] - fa10 [R(56) 32-0] = 46 496 559.1 (5.0) kHz
![](/documents/20126/60632397/CCL13+Recommendation+1+Table+4.png/5cd9c218-881f-37f0-12ae-b212f01a075f?t=1632824240197)
DOI : 10.59161/CCL2007REC1E
The reader should note that the official version of this Resolution is the French text