Temperature-dependence of the Kerr effect of chloromethanes

Abstract

Measurements of the Kerr effect (electric birefringence) are reported for the four chloromethanes (CH₃CI, CH₂CI₂, CHCI₃, CCI₄) in the vapour phase over a range of temperature (260–370 K). For CCI₄, the second hyperpolarisability γ^K is found to be (1.23 ± 0.04)× 10^–60 C⁴ m⁴ J^–3, in reasonable agreement with other nonlinear optical measurements. For CH₂CI₂, a polarisability anisotropy parameter (α₃₃–α) is determined to be (–0.68 ± 0.08)× 10^–40 C² m² J^–1, demonstrating the inadequacy of the bond additivity approximation. The first hyperpolarisabilities β^K of CH₃Cl, CH₂Cl₂ and CHCl₃ are relatively small and therefore poorly determined, indicating that hyperpolarisability contributions to the Kerr effect of dipolar molecules may in general be less significant than has previously been suggested.