Several recent investigations have contributed importantPresent knowledge of the refractive index of air is reviewed. cations that the standard adopted in 1953 on the basis of Barrel1 and Sears' measurements should be changed, but new experiments aiming at reducing the present uncertainty of new information on the dispersion of air, which has made it possible to derive an improved dispersion formula for standard ( n -1). x I O 8 = 8342.13 + 2406030 (130 -u2)-, + the absolute values there are as no definite + 15997 (38.9 -U')-', ab&t f 5 x 10-8 would be desiiable.where U is the vacuum wave-number in pm-l. The deviations Metrologia 12 from the 1953 formula are small and practically negligible in most spectroscopic work.An equation for the dependence of refractivity on temperature and pressure based on theoretical considerations has been derived. For the range of atmospheric conditions normally found in a laboratory the equation can be approximated by the formula with p in torr, t in "C, and (nl ) s given by the dispersion formula for standard air.The effect of carbon dioxide and water vapour is discussed. From Erickson's dispersion data for water vapour, combined with Barrel1 and Sears' absolute measurements, one obtains the equation ncPfntp = -f (5.722 -0.0457 ua) x for the difference in refractive index of moist air, containing f torr of water vapour, and dry air at equal temperature and total pressure. The equation is valid for visible radiations and normal atmospheric conditions.
The differences between observed and theoretical values of level intervals within the n = 2 complex in ions isoelectronic with Li, Be, 0 and F have been studied as functions of Z. The theoretical values are based on the tables of Cheng, Kim and Desclaux. For spin-orbit intervals, u(theor) is taken as their multiconfiguration Dirac-Fock value with Breit correction (MCDF + B), for other intervals within the same configuration the Z-independent correlation energy from Cheng, Froese Fischer and Kim is added, and for interconfiguration intervals a Lamb-shift correction is also included, obtained by transforming the values of Cheng et al. into a smooth function of Z. The difference U (obs) -U (theor) is then expressed by the formula A + B ( Z -C)-' t a(Z -s)", where the first two terms account for the residual correlation energy and the last term comprises all additional relativistic and radiative corrections. In a few cases we had t o use two such terms with opposite sign and exponents differing by 2 to 3 units. The constants A , B, C, a and x are adjusted to fit the observations within their error limits. As compared to a fitted polynomial, the present formula is much better suited for extrapolation and provides a sharper test of the experimental data, especially at the high2 end of a sequence. It has revealed a number of incorrect line identifications in the Be sequence. The results of the analyses are summarized in tables of recommended level values and wavelengths, extending to Z = 36 and in some cases to Z = 4 2 . The wavelengths obtained for the resonance lines in the Be, 0 and F sequences may become useful as wavelength standards.shown in Table IV. We have chosen the component 2P,,2-2S,,2 for which relativistic effects are largely cancelled because of
No abstract
This is a compilation of atomic lines with accurately known wavelengths covering the range from 15 Å to 25000 Å. The tables are a fairly complete record of available spectrum lines that meet the requirements for useful references with regard to wavelength accuracy and intensity. In general, wavelength uncertainties range from 0.0001 Å to 0.002 Å. Section 1, λ > 2000 Å, gives λair and λvac for 3341 lines belonging to thirteen different spectra of ten elements. Section 2, λ < 2000 Å, contains 2091 lines belonging to 59 different spectra of 28 elements. The lines of section 2 are listed both by spectrum (i.e. element and ionization stage) and in a finding list arranged in order of decreasing wavelength. Detailed explanations of the data and the sources used for the compilation are included.
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