Nonresonant Absorption of Symmetric Top Molecules. Shape of the Nonresonant Spectra

Abstract

The nonresonant or relaxation absorption spectrum was mapped out for the symmetric top molecules CH3F, CH3Cl, CH3Br, CH3I, CH3CN, CHF3, CClF3, and (CH3)3N. A cavity method was used to determine the absorption at several frequencies in the range 1200 to 24 000 Mc at pressures up to 2 atmos unless limited by the vapor pressure. Absorption due to the rotational lines was found to be important unless the frequency and pressure were kept sufficiently low. The results for CClF3 and (CH3)3N closely fit the Debye equation and lead to an accurate evaluation of the dipole moment, namely, 0.500×10-18 esu and 0.601×10-18 esu, respectively. The nonresonant spectra of the remaining molecules, which have larger dipole moments, deviate from the Debye shape in a manner that is characteristic of a distribution of line widths.