An investigation of the extra-photographic infrared region of Ge i utilizing electrodeless discharge tubes containing germanium tetraiodide, a grating spectrometer, and a lead sulfide detector has yielded 117 lines, observed between 11 252 and 23 922 Å. Subsequent interferometric determinations of 30 lines between 11 252 and 19 284 Å were carried out by scanning the circular fringes of a Fabry–Perot interferometer across the spectrometer slit to achieve accuracies of from 0.001 to 0.003 Å in this region. The motivation for this investigation came from the knowledge that the solution of difficulties which Andrew and Meissner [ J. Opt. Soc. Am. 49, 146 ( 1959)] encountered in establishing the levels of the 4s2 4p nf configurations of Ge i lay in the extra-photographic infrared. Of the 12 levels belonging to the 4p4f configuration they established only two by as much as a single pair of transitions; leaning heavily on the theory, they identified five others by a single transition each and predicted the positions of the remaining five. This investigation confirmed the tentative levels and established the missing levels which were found to lie close to their calculated positions. Similarly, values of 4d 3F4, 5f, 6f, and 7f 3G5, previously estimated by Andrew and Meissner with an uncertainty of ±5 cm−1, were verified and established to within ±0.1 cm−1. New values for the 6p 3D3 and 6p 1S0 levels were obtained. Also included are photographic grating measurements of a number of the weaker lines of Ge i not previously observed in the wavelength range 5006–10 858 Å which were obtained from 12 to 14 h exposures with electrodeless discharge tubes containing germanium oxide and neon.
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