FORCE FIELD AND NORMAL COORDINATES OF CYCLOPROPANE-H6 AND -D6

Force constants and normal coordinates are reported for the cyclopropane molecule. Recently determined data on all the fundamental vibration frequencies and E′ Coriolis zeta constants of cyclopropane-H5 and -D6, as well as zeta constants for the E″ species of C3H6, were used to refine to the A1′ and E′ species force constants with one constraint, and to the A2″ and E″ species force constants with two constraints. In the A1′ and E″ species, predictions of the hybrid orbital model are fulfilled; in the A2″ and E″ species, there are insufficient data to test the model. The results have been used to predict the fundamentals of cyclopropane-D5 (present as isotopic impurity in our sample of C3D6), to compute the observed intensity perturbation arising from Coriolis interaction between the ν10 and ν11 fundamental vibrations in cyclopropane-D6; and to calculate centrifugal distortion constants for C3H6. The good agreement with experimental observations in each case acts as a check on the accuracy of our derived force field. The choice of valence symmetry coordinates, either avoiding or including the ring angle redundancy, is briefly discussed. © 1969.