Re-examination of the vibrational force fields of trans- and cis-1,3,5-hexatriene: Effect of electron correlation, transferability of scale factors and correspondence of normal modes between the two isomers

Abstract

Abstract Ab initio molecular orbital calculations of the structures and vibrational force fields of trans- and cis -1,3,5-hexatriene are performed at the Hartree-Fock (HF) and the second-order Moller-Plesset perturbation (MP2) levels with the 6-31G ∗ basis set. Scale factors for force constants are optimized with reference to the observed vibrational frequencies of the trans isomer, and the transferability of the scale factors between the trans and cis isomers is examined. The scale factors for the in-plane force constants obtained at the MP2/6-31G ∗ level are transferable between the trans and cis isomers. However, the scale factors for the out-of-plane force constants obtained at the HF/6-31G ∗ level are better in transferability than those obtained at the MP2/6-31G ∗ level. Correspondence between the normal modes of the trans and cis isomers is examined by calculating the pseudo-Duschinsky rotation matrix. Mode-to-mode correspondence is easily understood by inspecting the elements of the pseudo-Duschinsky rotation matrix.