Molecular second- and third-order polarizabilities from measurements of second-harmonic generation in gases

The temperature dependence of dc electric-field-induced optical second-harmonic generation has been measured for CH₄, CH₃F, CH₂F₂, CHF₃, CF₄, CClF₃, and CBrF₃. For each molecule, experiments yield the second-order polarizability (-2;, ) and the third-order polarizability (-2; 0, , ). Both independent nonzero spatial components of each are measured. The bond-additivity model is shown to work well (15%) for third-order polarizabilities but poorly (discrepancies of about a factor of two) for second-order polarizabilities.