Measurements of nonlinear optical polarizabilities for twelve small molecules

Second- and third-order nonlinear optical polarizabilities for a number of small molecules—${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, CO, NO, C${\mathrm{O}}_2$, ${\mathrm{H}}_2$O, ${\mathrm{H}}_2$S, N${\mathrm{H}}_3$, S${\mathrm{F}}_6$, (C${\mathrm{H}}_3$)${}_2{}^{}{}_{}{}^{}\mathrm{O}$, and C${\mathrm{H}}_3$OH—are derived from measurements of the temperature dependence of dc-electric-field-induced optical second-harmonic generation in the gas phase. Agreement with related measurements (where available) is generally adequate, but the results of theoretical calculations taken from the literature are in poor agreement with the experimental data. Consideration of the present results for ${\mathrm{H}}_2$O together with liquid-phase measurements by Levine and Bethea offers a means of investigating intermolecular interactions in liquid water. The bond-additivity approximation applied to ${\mathrm{H}}_2$O, (C${\mathrm{H}}_3$)${}_2{}^{}{}_{}{}^{}\mathrm{O}$, and C${\mathrm{H}}_3$OH yields surprisingly good fits of the dipole moment, linear polarizabilities, and second- and third-order nonlinear polarizabilities to experimental data.