Intermolecular potential and width of pressure broadened spectral lines. IV. Influence of the nonrigidity of the molecules; diatomic molecules case

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Abstract
The influence of the nonrigidity of two colliding molecules on the infrared linewidths of the absorbing one is studied for the same rotational transition in various vibrational bands. For monatomic perturbers (Ar, Xe, Kr), the isotropic part of the potential energy is the main broadening mechanism in the vibrational bands of HCl and describes the large observed variation from the 0–0 to 0–2 vibrational bands. On the other hand, for couples of diatomics (HCl–HCl and CO–N2), the long range of the electrostatic contribution to the potential prevents the previous effect from occurring, and hence, less important variations appear for the calculated linewidth from one vibrational band to another. This is in agreement with the experimental results. Moreover, in this case further investigation displays another effect for the first few rotational lines due to the influence of the vibration‐rotation coupling on the broadening mechanism.