Measurements of the second hyperpolarizabilty of argon, methane, carbon tetrafluoride, and sulfur hexafluoride

The second hyperpolarizabilities {dollar}\gamma{dollar} have been measured at {dollar}\lambda{dollar} = 632.8 nm for argon (Ar), methane (CH{dollar}\sb4{dollar}), carbon tetrafluoride (CF{dollar}\sb6{dollar}), and sulfur hexafluoride (SF{dollar}\sb6{dollar}) by means of the dc Kerr effect in the gas phase. Measurements were made over a range of densities and extrapolated to the zero density limit. The results obtained have an uncertainty of 1.7%, 1.1%, 0.8%, and 0.5% for SF{dollar}\sb6{dollar}, CF{dollar}\sb4{dollar}, Ar, and CH{dollar}\sb4{dollar}, respectively. A comparison with other dc Kerr results shows our results to be the most accurate to date, thereby providing a better standard for judging quantum chemistry calculations of {dollar}\gamma{dollar}. The difference between the dc Kerr and electric-field-induced second harmonic generation (ESHG) vibrational hyperpolarizabilities, ({dollar}\rm \gamma\sb{K}\sp{V} - \gamma\sb{E}\sp{V}{dollar}), has been determined for CH{dollar}\sb4{dollar}, CF{dollar}\sb4{dollar}, and SF{dollar}\sb6{dollar}. The result for CH{dollar}\sb4{dollar} is found to be in good agreement with recent calculations by Bisho