Absolute measurement of the hyperfine splittings of six molecular I-127(2)lines around the He-Ne/I-2 wavelength at lambda approximate to 633 nm

With the aid of two diode-laser narrowband spectrometers around 633 nm, we report the measurement of the iodine hyperfine components of the R(60) 8-4, R(125) 9-4 and P(54) 8-4 transitions located -12 GHz from the classical re d He-Ne laser stabilized on the R(127) 11-5 transition of I-127(2), the P(3 3) 6-3 transition roughly -1 GHz away, the P(39) 6-3 transition 3.4 GHz abo ve, and the R(59) 8-4 and P(53) 8-4 transitions roughly 19 GHz above. The D oppler-free absorption signals were resolved using a third-harmonic detecti on technique and hyperfine frequency splittings were measured by beat-frequ ency techniques. The individual hyperfine transitions were linked to a 633 nm He-Ne laser by direct frequency measurements up to 16 GHz. The experimen tal standard uncertainty was typically below 5 kHz (i.e. relative uncertain ty <1 x 10(-11)).