Knowledge Bank

Quantitative infrared intensity measurements on HCl, HBr, and NO have been carried out by two independent experimental methods. In one group of tests an infrared-inactive gas was used to produce sufficient pressure-broadening of the rotational lines to permit quantitative measurements with a standard infrared spectrometer. In another series of investigations, the desired experimental conditions were obtained by the judicious use of self-broadening. The concordance between values for the integrated absorption obtained by the two methods was found to be within the limits of experimental error. The results for HCl are in good agreement with the numerical values reported by other $investigators.1$ For pressures not exceeding 10 atm, the experimentally determined absorption measurements are correlated quantitatively by the use of theoretical relations derivable from the dispersion formula for rotational line width. By carrying out numerical calculations, with the rotational half-width treated as a variable parameter, a direct comparison between calculated and observed infrared absorption has been used to determine rotational half-widths. Lower limits for the rotational half-widths have been determined by using Elasser's $treatment2$ for equally spaced and equally intense rotational lines. Representative results of intensity and line-width measurements are summarized in Table 1. [FIGURE] $\mathrm{<mrow\; data-mjx-texclass="ORD">\ast </mrow>}$ The pressure corresponds to the equivalent pressure of ideal gas. (1) $\alpha F=$ integrated absorption for the fundamental vibration-rotation band. (2) $\alpha 0=$ integrated absorption for the first overtone. (3) $\delta F=$ rotational half-width of the fundamental for self-broadening. (4) $\delta O=$ rotational half-width of the first overtone for self-broadening.