Measurements of nonlinear optical polarizabilities for some halogenated methanes: The role of bond-bond interactions

Abstract

Second- and third-order nonlinear optical polarizabilities for a number of halogenated methane molecules—C${\mathrm{Cl}}_4$, CH${\mathrm{Cl}}_3$, C${\mathrm{H}}_2$ ${\mathrm{Cl}}_2$, C${\mathrm{H}}_3$Cl, C${\mathrm{H}}_4$, C${\mathrm{Cl}}_2$ ${\mathrm{F}}_2$, and C${\mathrm{Cl}}_3$F—are derived from measurements of the temperature dependence of dc-electric-field-induced second-harmonic generation in the gas phase. Such data are now available for all twelve molecules: $C{X}_n{Y}_{4-n}$ with $X, Y=\mathrm{F},\mathrm{C}\mathrm{l},\mathrm{H}$. While the bond additivity approximation provides an excellent fit to the third-order polarizability data for this set of molecules, the fit for the second-order polarizabilities is poor. This poor fit can be understood on the basis of bond-bond interactions, and inclusion of an estimate of these contributions greatly improves the consistency of fit to the second-order polarizability data.