Equilibrium structures and in-plane harmonic force fields of ethylene, trans 1,3-butadiene, and all-trans 1,3,5-hexatriene were investigated with the aid of ab initio Hartree-Fock (SCF) calculations applying basis sets of DZ+P and TZ+P quality. The most interesting parts of the force fields, namely those involving stretching vibrations of the conjugated carbon backbone, were subsequently reevaluated including electron correlation at the coupled pair functional (CPF) level. We demonstrate that electron correlation has a significant influence not only on the degree of bond alternation in the ground state equilibrium structure but simultaneously leads to an increase in absolute value of all off-diagonal stretch-stretch coupling constants within the carbon backbone.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry