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: $C{X}_{n}{Y}_{4\ensuremath{-}n}$ with $X, Y=\mathrm{F},\phantom{\rule{0ex}{0ex}}\mathrm{C}\mathrm{l},\phantom{\rule{0ex}{0ex}}\mathrm{H}$. 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.