First Spectra of Chlorine, Bromine, and Iodine in the 18–40-μm Region

Use of liquid-nitrogen-cooled lead sulfide detectors has permitted the extension of observations of the first spectra of the halogens in the infrared region as far as 4.0 μm. Descriptions, comprising wavelengths, wave numbers, intensities, and classifications, are presented that serve to close the gap between the upper wavelength limit of the detailed published analyses of these spectra at about 2.5 μm and the groups of recently classified lines near 4 μm, and also to report newly observed lines in the 1.8–2.5-μm region made accessible by detectors of improved response characteristics. Listed wavelengths of observed and identified lines are calculated from established values of the energy levels. The descriptions should facilitate the identification of halogen lines in mixed spectra excited in electrodeless tubes containing halogen compounds.