Absorption Spectrum of Hydrogen Chloride

Abstract

THE unexpected satellites which Imes (Astrophysical Journal, November, 1919) found beside each line in the HCl absorption band at 1.76μ, and which measurements of his curves show to have an average wave-length 16 ± 4 Å, longer than the lines which they accompany, are readily accounted for as due to the heavier of the two isotopes, atomic weights 35 and 37, of which Aston (Phil. Mag., vol. xxxix., p. 611, 1920) has shown ordinary chlorine to consist. An approximate theory shows the wave-length of the band centre to vary as the square root of the effective mass, where m₁ is the mass of the hydrogen nucleus and m₂ that of the chlorine atom. Taking m = 35/36 for the lighter and 37/38 for the heavier isotope, the calculated difference between the wavelengths of corresponding lines for the two isotopes comes out 13 Å. This is much larger than the differences of about 0.004 Å. which have been found between lines of the isotopes of lead (Aronberg, Astrophysical Journal, vol. xlvii., p. 96, 1918, and Merton, Roy. Soc. Proc., A, vol. xcvi., p. 388, 1920).