Geoffrey L. D. Ritchie

Quadrupole moments of benzene, hexafluorobenzene and other non-dipolar aromatic molecules

The electric field-gradient birefringence method for determining molecular quadrupole moments, originally developed and applied to gases by Buckingham, has been extended to the study of nondipolar molecules in solution. Equipment developed for this purpose is described and infinite-dilution molar field-gradient birefringence constants at 298 K and 632.8 nm are reported for benzene, 1,3,5-trimethylbenzene, hexamethylbenzene, 1,3,5-trifluorobenzene and hexafluorobenzene as solutes in carbon tetrachloride. Analysis of results yields the molecular quadrupole moments, which are discussed in relation to the charge distributions in these molecules. The prediction that the quadrupole moments of benzene and hexafluorobenzene are opposite in sign is verified and the nature of molecular interactions involving these molecules is considered.

Temperature dependence of electric field-gradient induced birefringence in carbon dioxide and carbon disulfide

Abstract Equipment for measurements of the electric field-gradient induced birefringences of gases and vapour is described, and results for CO 2 and CS 2 over ranges of temperature (≈ 290–440 K) and pressure (up to 616 kPa) are reported. Analyses of the data show that at 300 K the temperature-independent contributions to the effects are small but not negligible (CO 2 , 2.4 ± 1.2%; CS 2 , −5.4 ± 3.5%) and definitive molecular quadrupole moments are obtained [(CO 2 , Θ = (−14.3 ± 0.6) × 10 −40 C m 2 ; CS 2 , Θ = (11.5 ± 0.5) × 10 −40 C m 2 ]. In the case of CO 2 , the results confirm the correctness of Buckingham and Dischs original single-temperature investigation of this species.

Polarizability anisotropies, magnetizability anisotropies and molecular quadrupole moments of acetylene, methylacetylene and dimethylacetylene

Measurements of the Rayleigh depolarization ratios (with and without inclusion of the vibrational Raman contributions), Cotton-Mouton effects and electric field-gradient induced birefringences of gaseous HCCH, HCCCH3 and CH3CCCH3 at 632.8 nm are analyzed in conjunction with other data to obtain reliable values of the polarizability anisotropies, magnetizability anisotropies and quadrupole moments of these molecules.

Molecular magnetic anisotropies from the Cotton–Mouton effect

Improved equipment for measuring magnetic and electric birefringence in liquids and solutions is described. Molar Cotton–Mouton constants and molar Kerr constants at 298 K and 632.8 nm are reported for four model species (benzene, carbon disulphide, chloroform and pyridine) dissolved in each of three non-dipolar solvents (carbon tetrachloride, cyclohexane and dioxan). A careful analysis of the data yields the magnetic anisotropies of the solutes and illustrates the advantages and limitations of dilute–solution birefringence measurements as a route to this quantity.

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.

Cotton—Mouton effect, magnetic anisotropy and molecular quadrupole moment of acetylene

Abstract New observations of the magneto-optical Cotton—Mouton effect of acetylene over a range of temperatures (≈293–442 K) are reported and analyzed to yield the magnetic anisotropy, Δχ, and the molecular quadrupole moment, Θ, of this species. The results, Δχ =(−3.94±0.25) × 10 −29 J T −2 and Θ = (20.1±0.6) × 10 −40 C m 2 , are in satisfactory agreement with the best values obtained by other experimental and theoretical methods. A discrepancy in relation to a previous study of this effect is resolved.

Temperature dependence of electric field-gradient induced birefringence (Buckingham effect) and molecular quadrupole moment of N2. Comparison of experiment and theory

Abstract Observations of electric field-gradient induced birefringence (the Buckingham effect) in gaseous N2 over a range of temperature (≈293–412 K) and pressure (up to ≈2000 kPa) are reported. Analysis of the data shows that the temperature-independent contribution to the effect is not negligible, and values of the molecular hyperpolarizability, B, and quadrupole moment, Θ, are derived. In the case of the quadrupole moment, the experimental value [Θ=(−4.97±0.16)×10 −40 C m 2 ] and a state-of-the-art ab initio value [Θ=(−4.93±0.03)×10 −40 C m 2 ] due to Halkier, Coriani and Jorgensen [Chem. Phys. Lett. 294 (1998) 292] are in excellent agreement.

Polarizability and magnetizability anisotropies of trimethylboroxine, Me3B3O3.: Comparison of boroxine and benzene ring systems

Abstract Measurements of the Rayleigh depolarization ratio (with and without inclusion of the vibrational Raman contribution) and the temperature dependence of the Cotton–Mouton effect of gaseous trimethylboroxine at 632.8 nm are analyzed to obtain experimental values of the polarizability and magnetizability anisotropies of this species. The polarizabilities and magnetizabilities of trimethylboroxine (Me3B3O3) and the symmetrically trimethylated benzene (Me3C6H3) are contrasted, and it is inferred that electron delocalization is substantially reduced, possibly even absent, in boroxine as compared to benzene.

Magneto-optical Cotton—Mouton effect of molecular oxygen. A comparison

Abstract Measurements of the magneto-optical Cotton—Mouton effect at 632.8 nm of O 2 ( 3 Σ) over a range of temperature (≈299–464 K) and pressure (up to 613 kPa) are reported and analysed. The study enables a useful comparison to be made of data obtained under different conditions by the two groups that have undertaken systematic measurements of this effect. Agreement between the experimental results and also the derived molecular properties is found to be satisfactory.

Molecular quadrupole moment of naphtalene

Measurements of the infinite-dilution molar field-gradient birefringence constant, Kerr constant and Cotton–Mouton constant of naphthalene as a solute in carbon tetrachloride at 298 K are reported. An analysis of the observations in conjunction with the known anisotropic molecular magnetisability of naphthalene yields the out-of-plane component of the quadrupole moment of this molecule. The quadrupole moments of naphthalene and benzene are related in proportion to the number of HC groups in these molecules, the result for napthalene (–45 × 10–40 C m2) being very close to 8/6 times that previously found for benzene (–33.3 × 10–40 C m2).