Using a sum-over-states procedure based on configuration interaction single
s /6-311++G**, we have computed the sum-frequency hyperpolarizability beta
(ijk)(-3 omega; 2 omega, omega) Of two small chiral molecules, R-monofluoro
-oxirane and R-(+)-propylene oxide. Excitation energies were scaled to fit
experimental UV-absorption data and checked with ab initio values from time
-dependent density functional theory. The isotropic part of the computed hy
perpolarizabilities, beta(-3 omega; 2 omega, omega), is much smaller than t
hat reported previously from sum-frequency generation experiments on aqueou
s solutions of arabinose. Comparison is made with a single-centre chiral mo
del. (C) 2000 Elsevier Science B.V. All rights reserved.