Nave et al. (1996) have determined very high-accuracy Ritz
wavelengths for 473 vacuum-ultraviolet
Fe II lines (927-1995 ). They
recommend the new values as standards, the uncertainties lying mainly in the range
0.0001 to 0.0003 . These new Fe II standards, like several sets of
high-accuracy wavelength determinations cited in our previous reports, depend on
visible-region Ar II reference standards from Norlén (1973). New measurements
of the Ar spectrum from a hollow-cathode discharge by Whaling et al. (1995) give Ar II wavenumbers systematically greater than Norlén's values by about 7 parts in
; adjustment of the new Fe II results of Nave et al. to the Ar II
wavenumber values of Whaling et al. would decrease the Fe II wavelengths by
0.00006 to 0.00014 .
The paper by Whaling et al. gives high-precision Ritz wavelengths for
hundreds of Ar II lines over the range 2225 to 5.33 
m. The wavenumber
uncertainties of most of the lines are less than 0.001 cm
, but the values are
uncorrected for any pressure shifts. A number of the lines in the range 3600 to
3.27 
m are indicated as especially appropriate for use as reference standards
because of their small pressure shifts. The systematic disagreement of 7 parts in
between these Ar II wavenumber determinations and those by Norlén ``is
roughly twice the uncertainty assigned to the wavenumbers in either experiment''
(Whaling et al. 1995). The indicated need for additional measurements is, according
to Nave et al., being met by experiments underway in other laboratories.