Intensities in the Harmonic Band of Hydrogen Chloride

Abstract

Measurement of absorption intensities.---The intensities of the first nine lines of the negative branch of the first harmonic absorption band of HCl at 1.76\ensuremath{\mu} have been measured with a prism spectrograph, using a galvanometer and thermo-relay to observe thermopile voltages. The positive branch, not being resolvable, was measured as a whole. The areas under the lines in a plot of percent absorption against frequency were obtained for 5 different tube lengths, namely 74.5, 25.0, 14.96, 9.90 and 4.88 cm and the integrated absorption coefficient of each line was calculated from the slope of the curve of area against tube length at the origin by methods developed by Bourgin. The probable error of the intensity measurements for the stronger lines was 6 percent.Correlation with theory.---A calculation is made of the intensity ratio of the band as a whole to that of the fundamental based on a solution of Schr\"odinger's equation obtained by Morse for an anharmonic oscillator, and the value so obtained is within 6 percent of the experimental value. A second order perturbation calculation based on harmonic oscillator functions did not give concordant results. An unpublished analysis of the effect of rotation on the relative intensities of the lines in a band by Kemble is given and the relative intensities calculated for this band, giving agreement with experiment within 5 percent.