Precise Measurement of Wavelengths in Infrared Spectra

The preci e measurement of infrared absorp tion spectra has been accomplish ed by using the " "hi telight frin ges of a Fabry-Perot interferometer in conjunctie n with atomic spcctrall in es. \\Tayelengths from the first spectra of neon, argon, krypton, a nd xenon were uscd for calibrating t he fringcs. The absorption spectra and the fringe systcm are recorded simultaneously by a two-pen r ecorder. One pen records t he higher orders of the frin ge system of visible ligh t as detected by a IP28 photomultiplier. The other pen r ecords the infrared absorption p ectrulll, which is detected by a PbTe cell . A measurement of t he distance from the center of the absorption line to t he neighboring maxima of t he fringe system determines t he line pos ition to a high precision. ' Vavelengths of infrared Jines can bc rn easured with a n error of one part in 500,000. Eight infl'arcd lines of mercury, seventeen l ines of krypton, and fi ' "C lines of xenon have been measured by this method. Tablcs are g iven of v is ible a nd in frared lines of the noble gases, which are useful for cal ibration.