New interferometric observations of Ar i in the photographic region*

The region 3173–11 672 Å of Ar i, originating in a microwave-excited electrodeless source, has been reinvestigated by means of a temperature-controlled Fabry–Perot interferometer in vacuum. There were a total of 307 lines compared with the primary standard, the 6057 Å line of 86Kr. The standard source was a microwave-excited electrodeless tube operated at the triple point of nitrogen. Spacers of 6, 30, 50, and 80 mm were used. The results are listed along with those of previous investigations in chronological order up to and including the most-recent publication of Norlén. In general, our wavelength values are lower than Norlén's. Most of the observed lines are suitable for use as standards; we identify those that are not suitable because they show doublet structure. Calculated wavelengths based on presently determined level values are also given along with the experimental wavelength values. Particularly for wavelengths greater than 7000 Å, the line sharpness is such that spacers longer than 100 mm may be used in future investigations.