Force constants of small molecules
The calculations ofnormal vibrations have two aspects. One is the use of calculated frequencies for the assignments of observed vibrational bands. In this case a deviation of several percent is permissible. Mizushima together with the author and co-workers have applied the Urey-Bradley force field to more than one hundred molecules and the assignments based on these calculations have been shown to be reliabJ.el, 2, The second aspect is to obtain accurate force constants. During the past few years the author and co-workers* have tried to obtain reliable and transferable force constants. This paper will review results so far obtained. Recently, Crawford, Overend, Scherer, Hisatsune et al. have madeextensive studies ~m the U rey-Bradley field. I t is a pleasure for the author to include these results in this review. For the potential function of molecules we started from the Urey-Bradley force field3 (UBFF) and tried to classify various molecules according to whether this type of force field is adequate or not.