Facultés Universitaires Notre-Dame de la Paix

The effect of charging on the longitudinal electronic and vibrational second hyperpolarizabilities of PA chains is investigated ab initio by characterizing chains with and without an explicit alkali atom (Li, Na, K) as dopant.

A classical electrostatic polarization scheme using the additive distribution procedure, and a supermol. approach, have been applied to determine the longitudinal polarizability of an all-trans hexatriene mol. in an infinite stretched fiber.The parameters have been derived from ab initio CPHF/6-31G calculations and the electrostatic scheme has been validated via comparison with supermol. ab initio results on small clusters.Upon packing the polarizability of all-trans hexatriene increases by 7%.This small increase results from the balance between the enhancement of the polarizability due to collinear packing and the reduction associated with lateral packing.

A review.This paper surveys successive methods which have been elaborated for simulating the hyper-Raman spectra of mols. and concentrates on a recently-developed Time-Dependent Hartree-Fock procedure.The later is illustrated by simulating spectra of small mols. for which exptl. spectra are available.