USE OF L-MATRIX TO OBTAIN RELIABLE AB-INITIO FORCE-CONSTANTS OF POLYATOMIC-MOLECULES - ETHYLENE AS A TEST SYSTEM

Direct use of experimental eigenvalues of the vibrational secular equa tion on to the ab initio predicted eigenvector space is suggested as a means of obtaining a reliable set of intramolecular force constants. This method which we have termed RECOVES (recovery in the eigenvector space) is computationally simple and free from arbitrariness. The RECO VES force constants, by definition, reproduce the experimental vibrati onal frequencies of the parent molecule exactly. The ab initio calcula tions were carried out for ethylene as a test molecule and the force c onstants obtained by the present procedure also correctly predict the vibrational frequencies of the deuterated species. The RECOVES force c onstants for ethylene are compared with those obtained by using the SQ M procedure.