Temperature dependence of the electrooptical Kerr effect: Anisotropic electric dipole polarizabilities of NH3, CH3NH2, (CH3)2NH, and (CH3)3N

The study that is reported here is concerned with the development of an experimental route to the four independent components of the electric dipole polarizability of species of Cs symmetry and, in particular, with the specification of the anisotropic polarizabilities of NH3, CH3NH2, (CH3)2NH, and (CH3)3N, for which a consistent set of data has not been available. It is shown that the four equations required to evaluate the four components of the optical-frequency (λ = 632.8 nm) polarizabilities of CH3NH2 and (CH3)2NH can be drawn from measurements of (1) the temperature dependence of the electrooptical Kerr effect, (2) the Rayleigh depolarization ratio, and (3) the refractive index of the gas together with (4) a simple bond-additivity model of the polarizability. The model uses the polarizabilities of the C3v species NH3 and (CH3)3N to estimate the off-diagonal polarizabilities of the Cs species CH3NH2 and (CH3)2NH. To this end, improved equipment has been used to record the vapor-phase Kerr effects of NH3, CH3NH2, (CH3)2NH, and (CH3)3N over ranges of temperature and pressure. An analysis of the data yields precise values of the anisotropic polarizabilities and, as a bonus, less precise values of the Kerr hyperpolarizabilities of all four molecules and provides a clear demonstration of the utility of the method.