COMPUTER-GENERATED PREDICTIONS OF IR AND RAMAN-SPECTRA OF ORGANIC-MOLECULES

Computer generated vibrational frequency predictions may be derived fr om ab initio molecular computations by introducing scaling procedures. We discuss two different scaling mechanisms, force constant scaling a nd direct frequency scaling. We express a preference for the second ch oice and we discuss some recent work based on direct frequency scaling . Due to advances in computer capability it is now possible to perform 6-31G computations on a molecule with a molecular weight of 267 wher eas just 10 years ago the upper limit consisted of 3-21G computations on molecules with molecular weights of around 50.