A comparison of molecular hyperpolarizabilities from gas and liquid phase measurements

The first and second hyperpolarizabilities ~b and g! 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 b and g for these molecules in the gas phase, and the HRS measurements show that the effective b of these molecules in the liquid is enhanced over the gas-phase value by a factor which varies from '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 b for HRS in the liquid phase. The results for CCl4, suitable as reference standards, are ^bVV 2 &518.660.7 au in the liquid phase and bxyz520.761.6 au in the gas phase. Comparison of measurements between hydrogenated and deuterated molecules indicates that vibrational contributions to b are small. © 1998 American Institute of Physics. @S0021-9606~98!03203-6#