The Intensity of Infrared Absorption Bands

Abstract

An experimental method of measuring the absolute intensities of infrared absorption bands in gases has been used in which the absorbed energy was measured directly by the volume change in the absorbing gas due to the heat evolution in it. The absorption cell was traversed by radiation from a specially constructed infrared monochromator arranged for evacuation. The incident energy density was found through a calibrated thermocouple and galvanometer and the optical characteristics of the monochromator. Measurements were made with various path-lengths of absorbing gas. The absorption was extrapolated to zero by using a logarithmic graph which has many advantages. Line-width forms were investigated. It was found that for CO, $\ensuremath{\alpha}=\ensuremath{\int}{\ensuremath{\alpha}}_{v}\mathrm{dv}$ was 1.18\ifmmode\times\else\texttimes\fi{}${10}^{13}$ for the fundamental vibration band at 4.66\ensuremath{\mu} and 1.54\ifmmode\times\else\texttimes\fi{}${10}^{11}$ for the harmonic. The corresponding Einstein coefficients and the amplitudes of electric moment were calculated. The results of the analysis show that the Lorentz collision broadening type of line shape satisfies the experimental data much better than other line shapes. The line widths of the fundamental and harmonic bands were observed as 0.10 and 0.12 ${\mathrm{cm}}^{\ensuremath{-}1}$ at atmospheric pressure which would arise from collision diameters of 5.5A and 6.1A respectively. These line widths are smaller than have been previously reported for infrared lines.