Vibrational effects on electric properties of cyclopropenone and cyclopropenethione

摘要

Vibrational contributions to the dipole polarizabilities and hyperpolarizabilities of cyclopropenone and cyclopropenethione are reported. Simultaneous calculations have been carried out for the respective; saturated and noncyclic counterparts of these molecules. The results have been analyzed and interpreted in terms of different structural and electronic features of the studied molecules: i.e., the oxygen-sulfur replacement, the saturati6n of the carbon ring, and the removal of the intramolecular strain. For static dipole po1arizabilities the vibrational contribution computed at the molecular equilibrium geometry can account for more than 10% of the total value for a given component of the tensor. Both the zero-point vibrational average and pure vibrational terms are important for most of the studied molecules. In the case of the first dipole hyperpolarizability the total vibrational correction is dominated by the pure vibrational term. The vibrational corrections to dipole polarizabilities show certain regularities which can be interpreted in terms of the electronic structure of the investigated molecules. Much less clear is the pattern of behavior for the first dipole hyperpolarizability. It has been found, however, that the analysis of these data is greatly facilitated by the separate consider~tion of the nuclear relaxation and curvature terms.. Limited study of the frequency dependence of the calculated vibrational correcti6ns shows that in the case of the dipole polarizability, they are almost quenched to zero. In contrast, at nonzero frequencies, the vibrational contribution to the first dipole hyperpolarizability tensor {3(-(tJ;w,O), which determines the so-called electro-optic Pockels effect, can be as important as the pure electronic term.