Measurement of the electric quadrupole moments of CO2 and OCS

The electric quadrupole moments of carbon dioxide and carbonyl sulphide have been measured via the technique of electric-field-gradient-induced birefringence (the Buckingham effect). Measurements for carbon dioxide span the temperature range 299.4 to 471.7 K, which allows for separation of the temperature-independent hyperpolarizability term from the temperature-dependent quadrupole term, yielding a quadrupole moment of Θ = (−14.31 ± 0.74) × 10−40 C m2, and a hyperpolarizability term of b = (−0.34 ± 0.19) × 10−60 C3 m4 J−2. Thermal decomposition of carbonyl sulphide at elevated temperatures restricted our measurements for this molecule to room temperature (302.1 K), yielding a quadrupole moment of Θ = (−0.984 ± 0.034) × 10−40 C m2, the hyperpolarizability term having been assumed to contribute negligibly.