Vibrational effects on electric properties of cyclopropenone and cyclopropenethione

Vibrational contributions to the dipole polarizabilities and hyperpolarizab ilities of cyclopropenone and cyclopropenethione are reported. Simultaneous calculations have been carried out for the respective saturated and noncyc lic counterparts of these molecules. The results have been analyzed and int erpreted in terms of different structural and electronic features of the st udied molecules: i.e., the oxygen-sulfur replacement, the saturation of the carbon ring, and the removal of the intramolecular strain. For static dipo le polarizabilities 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 cor rection is dominated by the pure vibrational term. The vibrational correcti ons to dipole polarizabilities show certain regularities which can be inter preted in terms of the electronic structure of the investigated molecules. Much less clear is the pattern of behavior for the first dipole hyperpolari zability. It has been found, however, that the analysis of these data is gr eatly facilitated by the separate consideration of the nuclear relaxation a nd curvature terms. Limited study of the frequency dependence of the calcul ated vibrational corrections shows that in the case of the dipole polarizab ility, they are almost quenched to zero. In contrast, at nonzero frequencie s, the vibrational contribution to the first dipole hyperpolarizability ten sor beta(-omega;omega ,0), which determines the so-called electro-optic Poc kels effect, can be as important as the pure electronic term. (C) 2001 Amer ican Institute of Physics.