STUDY ON THE IR BAND INTENSITIES OF CYCLOPROPANE

The i.r. absorption intensities of cyclopropane-h6 and -d6 were measured in the gas phase using the pressure broadening technique. The obtained band intensities were analysed in order to determine the intensity parameter (∂p/∂Sj) with the help of information from the Coriolis interaction and CNDO/2 calculation. It has proved that the Coriolis interaction can offer important information even for a couple of bands which are mutually removed far away. In case of C3H6, despite 400 cm-1 distance between the ν9 and ν10 bands, the product ζz(∂px/∂Q9a )(∂py/∂Q10b) has been determined as positive. In this way the sign of (∂p/∂Qi) has been clearly decided for cyclopropane, and consequently the value of (∂p/∂Sj) has been definitely determined. Further, by investigating the present results with those previously obtained, for many other related molecules, the following general rule has been found about the relationship between the sense of displacement vector of hydrogen atom group and the enhanced dipole moment vector induced thereby. Namely, the directions of these two vectors are opposite for the stretching vibrational modes and the same for almost all deformation vibrational modes of hydrogen atoms. © 1979.