Pressure Broadening of Symmetric-Top Molecules in the Millimeter-Wavelength Region

Abstract

Self-broadened and foreign-gas-broadened widths of a number of millimeter lines of the symmetric-top molecules CH3F and CHF3 have been measured and compared with values calculated by Anderson's and Murphy and Boggs' theories of pressure broadening. The lines studied are the J = 2 → 3, K = 0, 1, 2 lines of CH3F, and the J = 6 → 7, K = 3, 4, 5, 6 lines of CHF3 at 300°K and the K = 5 and 6 lines at 200°K. The broadening of the J = 2 → 3, K = 2 line of CH3F by CO2 at 300°K was also studied. With one exception where Anderson's theory and experiment are in good agreement, viz., the J = 2 → 3, K = 2 line of CH3F (300°K), this theory gives results greater than the experimental values. Although the theory of Murphy and Boggs is over all in better agreement with experiment, here too a number of discrepancies appear. Neither theory gives the observed dependence of the linewidth on the rotational quantum number K.