Microwave Spectra of Molecules Exhibiting Internal Rotation. I. Propylene

Abstract

The microwave spectrum of propylene, CH₃CH:CH₂, has been investigated in the region 17–36 kmc. Measurements have been made on the normal isotopic species and on the H₃CC¹³H:CH₂ species. Most of the observed lines are split slightly as a result of internal rotation. These splittings have been satisfactorily analyzed by the methods of Hecht and Dennison, giving an internal potential barrier of 692.4±6 cm^—1 or 1978±17 cal/mole. Principal moments of inertia (in units of amu A²) are 10.973, 54.312, and 62.175 for H₃CCH:CH₂ and 11.160, 54.318, and 62.382 for H₃CC¹³H:CH₂. The electric dipole moment has a magnitude of 0.364 D and makes an angle of 8° with the a principal axis. With reasonable assumptions concerning the location of the hydrogen atoms the remaining structural parameters are: r_CC=1.488 A, r_C:C=1.353 A, ≤ CCC=124°45′.