Direct Method of Measuring Molecular Quadrupole Moments
1959; American Institute of Physics; Volume: 30; Issue: 6 Linguagem: Inglês
10.1063/1.1730242
ISSN1520-9032
Autores Tópico(s)Atmospheric Ozone and Climate
ResumoAn experiment whose object is the determination of permanent molecular quadrupole moments is suggested. It is analogous to those used in measurements of electro-optical Kerr constants, but the uniform electric field proportional to the applied voltage V is replaced by the field gradient of a square four-wire condenser. If the wires at x=±a are at a potential V relative to those at y=±a, then the field gradient on the z axis will tend to orient quadrupolar molecules so that a fluid in the condenser will become doubly refracting. The induced anisotropy in the refractive index of a gas is shown to be first order in the applied voltage and of the form nx—ny=[B+(A/T)]V, while in the Kerr effect it is second order in V, and is given by nx—ny=[C+(D/T)+(E/T 2)]V2. The constant A is proportional to the molecular quadrupole moment and to the anisotropy in the polarizability, while B is proportional to the quadrupole moment induced in a molecule by a uniform field. In spherical molecules A, D, and E are zero. Calculations indicate that measurements of nx—ny, leading to accurate molecular quadrupole moments, should be practicable with present-day equipment. The theory of the effect in dense media is also developed.
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