A COMPARISON OF MOLECULAR HYPERPOLARIZABILITIES FROM GAS AND LIQUID-PHASE MEASUREMENTS

The first and second hyperpolarizabilities (beta and gamma) of eight m olecules at a fundamental wavelength of 1064 were measured by gas-phas e electric-field-induced second-harmonic generation (EFISH), gas-phase hyper-Rayleigh scattering (HRS), and liquid-phase HRS experiments. Th e EFISH measurements give accurate values of beta and gamma for these molecules in the gas phase, and the HRS measurements show that the eff ective beta of these molecules in the liquid is enhanced over the gas- phase value by a factor which varies from approximate to 0.4 to 2.0, o ver and above the Lorentz local field factors. Combining all of the me asurements provides an accurate, absolute determination of the effecti ve beta for HRS in the liquid phase. The results for CCl4, suitable as reference standards, are [beta(VV)(2)](1/2)=18.6+/-0.7 au in the liqu id phase and beta(xyz)=20.7+/-1.6 au in the gas phase. Comparison of m easurements between hydrogenated and deuterated molecules indicates th at vibrational contributions to beta are small. (C) 1998 American Inst itute of Physics. [S0021-9606(98)03203-6].