Spectra of the Noble Gases in the 4-μ Region*

The spectra of neon, argon, krypton, and xenon have been observed in the wavelength region 3.8 to 4.1 μ, using an infrared spectrometer equipped with cooled lead sulfide detector. The most important observations are of the near-hydrogenic and closely pair-coupled 4f–5g transitions, which establish for the first time all the 5g level pairs lying below the first ionization limit of each element. A detailed investigation of the theoretically predicted 4f–5g energy levels and relative line strengths shows very good agreement with observation. Various p–s, p–d, and d–f transitions have been identified, the most significant new result being the establishment of the level pairs 5f[412]4,5 and 5f[312]3,4 of Ne i, which previously had been only estimated.