Rotation-Vibration Spectra and the Molecular Constants of Cyclopropane and Cyclopropane-d6

The parallel fundamental infrared bands of cyclopropane at 3101 cm—1 and cyclopropane-d6 at 2336 cm—1 have been studied at high resolution. The ground-state rotational constants B″, whose values are found to be 0.6696±0.0028 and 0.4630±0.0023 cm—1, respectively, yield a value for the C – C distance of 1.524±0.014 A and a functional relationship between the C – H distance and the HCH angle. If the C – H distance is assumed to be 1.07 A, the HCH angle appears to have a value just above 120°. A normal-coordinate treatment yields force constants and eigenvectors for vibrations of species A1′, A2″, E′, and E″. Zeta constants of vibration-rotation interaction for species E′ have been calculated for both cyclopropane and cyclopropane-d6.