Knowledge Bank

The use of noble-gas atomic emission lines for spectrometer calibration and wavelength inter-comparisons has been discussed at a number of previous symposia. The recent book by Rao, Humphreys and $Rank1$ contains most of the material available at the time of its publication. The actual spectral range covered by lines in this category is from a little below the lower limit of the visible spectrum near $4000\backslash AA$ngstroms to wavelengths about tenfold greater near 4 microns in the infrared. Utilization of high orders of the more intense lines brings them within the range of usefulness for the molecular spectroscopist. The most important recent development has been associated with the availability of isotopes of the noble gases of even mass number. Spectra of such isotopes are entirely free of hyperfine structure and, of course, of isotopic structure if single species are used in sources. The isotopes subject to most intensive investigation so far are $\mathrm{<mrow\; data-mjx-texclass="ORD">86</mrow>}$Kr, whose spectrum includes the international primary standard both for metrology and spectroscopy, $\lambda vac.6057.80211$ {\AA}, $\mathrm{<mrow\; data-mjx-texclass="ORD">136</mrow>}Xe$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">20</mrow>}Ne$. Recently determined wavelengths from the first two of these will be displayed or referenced.