Wavelength of the 3.39-μm laser-saturated absorption line of methane

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Abstract
The wavelength of the 3.39‐μm line of methane has been measured with respect to the Kr86 6057‐Å standard by using a frequency‐controlled Fabry‐Perot interferometer. We have exhaustively studied systematic offsets inherent in the experiment, including effects due to asymmetry of the Kr standard line. Lacking a convention relating the defined Kr wavelength 6057.802 105 Å to observables of the krypton line (e.g., center of gravity or fringe maximum intensity point), we report two methane wavelengths: λmax I=33 922.314 04 Å and λcg=33 922.313 76 Å. Both results have an uncertainty of δλ=±1.2×10−4 Å or δλ/λ=±3.5×10−9. Multiplication by the frequency measurement of the preceding letter gives the speed of light, ccg=299 792 456.2(1.1) m/sec.