ИСТИНА

The simplicity of the scaling procedure made it extremely popular in recent years. It was shown that for many molecular fragments scale factors (within a given level of quan-tum-mechanical method) are approximately constant in a wide range of similar molecules. Force constant scaling factors were obtained for different sets of coordinates and quan-tum-mechanical methods, which in most cases allows to approximate experimental fre-quencies with a reasonable degree of accuracy. Introduction of the complete system of internal coordinates is the most tedious and time-consuming procedure, especially for the large molecular systems. We have proposed the procedure of direct scaling ab initio force field matrix in Cartesian coordinates, thus avoiding the need in internal coordinate representation. The numerical implementation of algorithm for the calculation of scale factors of molecular force filed expressed in Carte-sian coordinates is reported. Compared to previous version of the algorithm1, direct reduc-tion by symmetry is applied, and use of experimental data on several isotopic species is allowed. Account for symmetry constraints may be done in a more efficient way since for the symmetric molecules it is possible to reduce the general inverse problem into a set of independent problems with smaller dimensions, one for each symmetry type. In this report we apply Cartesian scaling to the indole and pyrrole molecules, and use additional experimental data available for deuterated molecules. Quantum mechani-cal calculations were performed with the program GAUSSIAN 03 (Revision B.03) pack-age. Calculations of scaling factors were carried out using special routine of the software package SPECTRUM which has been supplied with the additional options mentioned in the previous section. The molecules of pyrrole and indole were chosen to demonstrate the efficiency of scaling procedure in Cartesian coordinates with account for symmetry.. 1 I. V. Kochikov, G. M. Kuramshina, A. V. Stepanova. – Int. J. of Quant. Chem., 2009, 109, 28-33.