Wavelengths and Energy Levels of Ar I and Ar II based on New Interferometric Measurements in the Region 3 400-9 800 Å

Wavelengths of 233 lines in the Ar I spectrum and 354 lines in the Ar II spectrum, excited in a water-cooled hollow cathode at a pressure of 0.2 torr, have been measured by means of a Fabry-Perot interferometer in the vacuum. Fourteen different etalon spacers between 5 and 70 mm in length, two pairs of interferometer plates and three different coatings have been used during the investigation. Reference lines have been obtained from a calibrated electrodeless lamp containing Kr86 at a pressure of 0.2 torr. By means of the measured wavelengths the values of 80 energy levels in Ar I and 153 levels in Ar II have been derived, the uncertainty of the relative values varying from a few tenthousandths to a few thousandths of a cm-1. For both spectra these level values have then been used to obtain calculated wavelengths, extending down to 1 557 Å in the case of Ar II. The levels of 3d and 5s of ArI, most of which are inaccessible in the photographic region, have been redetermined relative to the new values of the 4p-levels by using the interferometric measurements in the photo-electric infrared published by Humphreys and Paul, Littlefield and Rowley, and Peck et al.