VIBRATIONAL AND ELECTRONIC 2ND HYPERPOLARIZABILITIES OF ALL-TRANS POLYSILANE CHAINS

The vibrational (gamma(L)(upsilon)) and electronic (gamma(L)(e)) longi tudinal second hyperpolarizabilities of increasingly large polysilane chains are determined at the Hartree-Fock 6-31G level by adopting both the double harmonic oscillator approximation and the infinite optical frequency finite field relaxation procedure. The relative importance of the electronic, Raman, infrared/hyperRaman and lowest-order anharmo nicity contributions to the second hyperpolarizability is evaluated fo r the most common nonlinear optical (NLO) processes. At the double har monic oscillator level of approximation the most contributing vibratio nal normal modes to gamma(L)(upsilon) are characterized as a function of the polysilane chain length. Comparisons with experimental and othe r theoretical studies are carried out in what concerns the infrared an d Raman vibrational spectra as well as the NLO properties of various o ligosilanes and polysilanes. (C) 1998 American Institute of Physics.