Microwave Linewidths of Symmetric-Top Molecules

Publisher Website
Google Scholar
Abstract
The Anderson—Tsao and Curnutte impact theory of pressure broadening is applied to microwave rotational lines of symmetric-top molecules. The effect of elastic and inelastic collisions on the optical cross section is examined. Simple but accurate expressions are obtained for microwave linewidths due to a variety of intermolecular interactions. The theory is applied to existing microwave linewidths, which happen to involve interactions between polar molecules. The theoretical width of the J = 1→2 line of PF3 is in good agreement with experiment, although the agreement is less satisfactory for the J = 0→1 line of CH3F and CHF3, and poor for the J = 1→2 line of CHF3. However, the theory satisfactorily accounts for widths of the NH3 3–3 inversion line broadened by CHF3 as well as other symmetric-top molecules.