Vibrational intensities and directions of the dipolar derivatives of the trans- C2H2X2 (X=F or Cl)

Ln-plane vibrational intensities and dipolar derivative directions of tmns- C2H2X2 (X=F or Cl) were calculated from a set of systematically planned ab initio calculations. The results reveal that the directions of the partial derivative p/partial derivative Q(1)'s are practically invariant to both, t he level of calculation and basis set change, in contrast to that found for the vibrational intensities. With the exception of the direction of the C- H stretching mode for trans-C2H2Cl2, all the others follow behaviors expect ed if simple chemical valency concepts are applied to the trans-dihaloethyl enes. Thus, the directions of the stretching and bending dipolar derivative s are almost parallel and perpendicular to the chemical bonds, respectively . These directions and the experimental vibrational intensities were used t o obtain the atomic polar tensors of the trans-dihaloethylenes. (C) 1999 El sevier Science B.V. All rights reserved.