ANALYSIS OF THE VIBRATIONAL STATIC AND DYNAMIC 2ND HYPERPOLARIZABILITIES OF POLYACETYLENE CHAINS

The RHF/6-31G longitudinal vibrational second hyperpolarizabilities of increasingly longer polyacetylene chains have been computed within th e double harmonic approximation. The [alpha(2)](0,0) contribution conv erges rapidly with chain length to an asymptotic limit 30% larger than its electronic counterpart. The [mu beta](0,0) term converges much mo re slowly. It is only 4% of the electronic term for C16H18, the longes t oligomer considered here, but the ratio is growing rapidly with chai n length.