Abstract

In the region 8200–2144 A the wavelengths or vacuum wave-numbers of seventy-three lines in the first spectrum and eleven in the second spectrum of cadmium have been measured relative to neon standards or to the mercury-198 spectrum or to both. The source for natural cadmium was a Beese lamp operated at 2.5–4.5 amp. For cadmium-114 the source was either a quartz Michelson lamp (plus 1.0 mm argon) operated under standard conditions or at lower temperature, or an electrodeless tube containing 0.5 mg of cadmium-114, 0.5 mg of mercury-198, and neon at 3 mm pressure. The use of cadmium-114 is preferable if the lines arising from SP combinations are to be used as secondary standards. For PD combinations the natural element is quite satisfactory. The characteristics of various sources are discussed. For the greater part of the observation required for this publication we have used the interferometer in vacuum; wave numbers so observed are unaffected by the refractive index of air and its changes with temperature, pressure, and constitution.

The vacuum interferometer and Michelson lamp were described in another paper by Kenneth B. Adams and Keivin Burns. [ K. B. Adams and K. Burns, J. Opt. Soc. Am. 46, 36 ( 1956)].

The wave numbers of mercury-198 measured by means of the vacuum interferometer have been compared with the wavelengths measured in air and converted to wave numbers by Edlen’s formula [ Transactions of the Joint Commission for Spectroscopy, J. Opt. Soc. Am. 43, 412 ( 1953)]. From 5790 to 2636 A the relative accuracy of the formula is confirmed. By differences in cadmium wave numbers the formula is checked from 6438 to 2288 A. Edlen’s formula is used throughout this paper wherever wavelengths in air are converted to wave numbers in vacuum or vice versa.

© 1956 Optical Society of America

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