Cotton‐Mouton Effect and Rotational Zeeman Effect in Dilute Gases — Two Complementary Methods for the Determination of Molecular Magnetic Properties

The first‐ and second‐order rotational Zeeman effect was investigated in isobutane. The magnetic‐field induced birefringence was measured at room temperature in several gases formed by axially symmetric molecules using pressures up to 1 bar. For benzene vapour these measurements were extended to higher temperatures. The susceptibility anisotropies obtained from the Cotton‐Mouton constants of the gases agree well with those measured directly by the rotational Zeeman effect which indicates that hyperpolarizabilities are negligible. The corresponding temperature independent contribution to the Cotton‐Mouton effect of benzene vapour proves to be less than 3% of the Cotton‐Mouton constant at room temperature.