Vibrational hyperpolarizability of SF6

Expressions are derived for the vibrational second hyperpolarizability ? v of SF6, in the static limit and for the nonlinear-optical processes of the dcKerr effect, electric-field-induced second harmonic generation (ESHG), and third harmonic generation (THG). These expressions give ? v in terms of vibrational transition dipole, polarizability, and first hyperpolarizability matrix elements (?,?,?). The matrix elements needed in the numerical evaluation of ? v are obtained from the literature and from the Raman scatteringmeasurements reported here. In the static limit it is found that ? v ?20 ? e , where ? e is the electronic contribution to ?. At optical frequencies ? v is still comparable to ? e in magnitude, and it shows significant frequency dependence.