First hyperpolarizabilities beta of carbon tetrachloride, carbon tetrafluoride, deuterated methane, and methane have been measured by hyper-Rayleigh scattering in gas and liquid phases. The gas-phase results for the coefficient beta xyz (atomic units) are 11.0 +/- 0.9 (CC14), 5.4 +/- 0.4 (CF4), 7.0 +/- 0.6 (CD4), 7.1 +/- 0.7 (CH4). Ab initio calculations are consistent with the measured values for CCl4 and CF4. A discrepancy between theory and experiment remains for CH 4, and is likely due to higher-order vibrational effects not accounted for in calculations. While the effective, liquid-phase beta for CCl 4 is 200% higher than in the gas phase due to collective scattering modes, the liquid environment has little effect on beta for the other molecules. CD4 and CH4 liquids exhibit free-rotor behavior. Liquid-gas comparisons for CF4, CD4, and CH4 show evidence that the Lorentz local-field corrections are inadequate in nonlinear optics. Through z-scan measurements, thermal lensing and/or absorption coefficients have been obtained for six molecules
