Vacuum Ultraviolet Spectrum of Neutral Silicon*

Measurements have been made on about 200 Si i lines in the region 1548 to 2000 Å excited by a low-pressure source, resulting in wavelength values with uncertainties of less than 0.0015 Å on the average. Of these vacuum ultraviolet wavelengths, 88 have been calculated by Radziemski and Andrew [ J. Opt. Soc. Am.55, 474 ( 1965)], and a comparison of measured and calculated values gives an average deviation of 0.0008 Å. A plot of the differences shows the scatter to be much greater than any systematic difference. This indicates that the calculated wavelengths are compatible with the set of Ge i lines used as standards in measuring the Si i lines. The new data have also led to an extension and a slight revision of the odd-level analysis. New measurements on some lines of C i, Ge ii, N i, and Si ii are also reported. Spectrograms were taken in the first order on a 10.7-m Eagle vacuum spectrograph with a reciprocal dispersion of 0.78 Å/mm. The source was an electrodeless discharge lamp containing SiCl4 and GeCl4 vapor with argon or helium carrier gas at a total pressure no greater than 0.5 torr.