Quantitative Line-Width Measurements in the Infrared. I. Carbon Monoxide Pressurized with Infrared-Inactive Gases

Abstract

Quantitative infrared‐intensity measurements on CO pressurized with gases such as H₂, He, and A have been carried out at room temperature. For pressures up to 100 psia the experimental absorption measurements are correlated quantitatively by the use of theoretical relations derivable from the dispersion formula. Thus, for a fixed value of the total pressure, the observed absorption is a linear function of the square root of the optical density. Similarly, at constant optical density, the absorption is a linear function of the square root of the total pressure. Using Elsasser's treatment for equally spaced and equally intense rotational lines, lower limits have been determined for the rotational half‐widths of CO broadened by various infrared‐inert gases. The determination of rotational half‐widths from spectroscopic measurements can be refined by allowing for the variation of integrated absorption per rotational line from one line to another in a given vibration‐rotation band. By carrying out numerical calculations, with the rotational half‐width treated as a variable parameter, a direct comparison between calculated and observed infrared absorption can be used to determine the rotational half‐width δ⁰ for pressures which are small enough to justify a treatment for nonover‐lapping rotational lines. In this manner it was found that (δ_F)H₂ = 0.077 cm⁻¹ atmos⁻¹, (δ_F)_A = 0.040 cm⁻¹ atmos⁻¹, (δ_O)H₂ = 0.063 cm⁻¹ atmos⁻¹. Here the subscripts F and O denote measurements on the fundamental and the first overtone, respectively. The subscripts H₂ and A identify the broadening agent used for study.