Effect of Foreign Gases on IR Absorption Bands of Polyatomic Molecules

Abstract

The effect of foreign gases (He, Ar, N₂ and CO₂) on IR vapour absorption bands corresponding to the vibrations of different symmetry is studied for some symmetric-and asymmetric-top molecules (chloroform, bromoform, trichlorethylene, chlorbenzene, naphthalene). It is shown that rotational P-, Q- and R-branches collapse and a single structureless bandshape appears when foreign gases are added at no more than 75 atm pressure of CO₂ or 175 atm of N₂. A conclusion is made that the contour variations in high pressure gas mixtures are satisfactorily interpreted by the J-diffusion model, i. e. these are related to an increase of hindering of free rotation at binary collisions that change both the direction and magnitude of the angular momentum of molecules. Difficulties appear in the J-diffusion model calculations of the whole absorption bandshape with

Key Words:

• Infrared
• Absorption bandshape
• High pressure
• Gas mixtue
• Dipole correlation
• function
• J-diffusion model