Vibrational hyperpolarizability of SF&

Expressions are derived for the vibrational second hyperpolarizability 1'" of SF 6' in the static limit and for the nonlinear-optical processes of the dc Kerr effect, electric-field-induced second harmonic generation (ESHO), and third harmonic generation (THO). These expressions give 1'" in terms of vibrational transition dipole, polarizability, and first hyperpolarizability matrix elements (f-L,a,/3). The matrix elements needed in the numerical evaluation of 1'" are obtained from the literature and from the Raman scattering measurements reported here. In the static limit it is found that 1'" :::::20 r, where r is the electronic contribution to y. At optical frequencies 1'" is still comparable to r in magnitude, and it shows significant frequency dependence.