A comparison of molecular hyperpolarizabilities from gas and liquid phase measurements

The first and second hyperpolarizabilities (beta and gamma) of eight molecules at a fundamental wavelength of 1064 were measured by gas-phase electric-field-induced second-harmonic generation (EFISH), gas-phase hyper-Rayleigh scattering (HRS), and liquid-phase HRS experiments. The EFISH measurements give accurate values of beta and gamma for these molecules in the gas phase, and the HRS measurements show that the effective 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, over and above the Lorentz local field factors. Combining all of the measurements provides an accurate, absolute determination of the effective 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 liquid phase and beta(xyz)=20.7+/-1.6 au in the gas phase. Comparison of measurements between hydrogenated and deuterated molecules indicates that vibrational contributions to beta are small. (C) 1998 American Institute of Physics. [S0021-9606(98)03203-6].