Temperature dependence of electric field-gradient induced birefringence (the Buckingham effect) in C6H6 and C6F6: comparison of electric and magnetic properties of C6H6 and C6F6

Observations of electric field-gradient induced birefringence (the Buckingham effect) in gaseous C6H6 and C6F6 over ranges of temperature (≈318–415 K) and pressure (up to ≈63 kPa) are reported. Analyses of the data show that at 300 K the temperature-independent contributions to the effects are not negligible (C6H6, −9.1±1.3%; C6F6, 7±5%) and definitive molecular quadrupole moments are obtained [C6H6, Θ=(−30.4±1.2)×10−40 C m2; C6F6, Θ=(28.3±2.1)×10−40 C m2]. Electric and magnetic properties of C6H6 and C6F6 derived from electro-optical and magneto-optical experiments are collated and compared in relation to the charge distributions in these species.