A. David Buckingham

Bio: A. David Buckingham is an academic researcher. The author has contributed to research in topics: Polarizability & Kerr effect. The author has an hindex of 6, co-authored 6 publications receiving 358 citations.

Rayleigh scattering depolarization ratio and molecular polarizability anisotropy for gases

Abstract: The depolarization ratio for Rayleigh scattering by 39 molecular species are reported for λ= 488.0, 514.5 and 632.8 nm. The literature has been critically surveyed for refractivities which are used in conjunction with the observed depolarization ratios to yield the anisotropy of the molecular polarizability of the molecules. Results are given for CO2, OCS, CS2, C2H6, C3H8, isobutane, cyclopropane, C2H4, allene, C2H2, methylacetylene, dimethylacetylene, spiropentane, cyclohexane, C6H6, C6H5F, 1,3,5-C6H3F3, C6F6, CH3CN, (CH3)2CO, CH3F, CH2F2, CHF3, CH3Cl, CH2Cl2, CHCl3, CF2Cl2, CH3Br, CH3I, t-butylchloride, t-butylbromide, ethylene oxide, (CH3)2O, (CH3)2S, H2S, SO2, N2, N2O and CO.

The electrostatic model of field gradients at nuclei. An application to hydrogen-bonded complexes of HCl

Abstract: An SCF wavefunction has been used to calculate the dependence of the electric field gradient at the Cl nucleus in HCl on external non-uniform fields. Analytic coupled Hartree–Fock and numerical methods have been used to find the series of response properties (generalised Sternheimer shieldings) for perturbation by a field and its first three gradients. These parameters have been used in an electrostatic model of the 35Cl quadrupole coupling constant in weakly bound complexes B⋯HCl, where B is a base such as H3N, HCN, CH3CN, H3P and OC. Slow convergence of the series explains the discrepancy between previously published values for the linear dependence of the Cl field gradient on an external uniform field.

Temperature-dependence of the Kerr effect of chloromethanes

Abstract: Measurements of the Kerr effect (electric birefringence) are reported for the four chloromethanes (CH3CI, CH2CI2, CHCI3, CCI4) in the vapour phase over a range of temperature (260–370 K). For CCI4, the second hyperpolarisability γK is found to be (1.23 ± 0.04)× 10–60 C4 m4 J–3, in reasonable agreement with other nonlinear optical measurements. For CH2CI2, a polarisability anisotropy parameter (α33–α) is determined to be (–0.68 ± 0.08)× 10–40 C2 m2 J–1, demonstrating the inadequacy of the bond additivity approximation. The first hyperpolarisabilities βK of CH3Cl, CH2Cl2 and CHCl3 are relatively small and therefore poorly determined, indicating that hyperpolarisability contributions to the Kerr effect of dipolar molecules may in general be less significant than has previously been suggested.

An ab initio investigation of N2⋯CO+

Abstract: Recent experiments have indicated that the interaction between CO+ and N2 is fairly strong; certainly stronger than would be expected from electrostatic considerations alone. We present calculations using ab initio molecular orbital theory that support the experimental findings, suggesting a binding between CO+ and N2 of the order of 100 kJ mol–1. However, most of this binding is the result of long-range interactions and there is little evidence for the formation of an incipient ‘chemical bond’.

Temperature dependence of the Kerr effect of dimethyl ether

Abstract: Measurements of the Kerr effect (electric birefringence) are reported for gaseous dimethyl ether over the temperature range 259–334 K. The dominant contribution is that in µ2(α33–α)(kT)–2; α33–α is the difference between the optical polarizability in the direction of the dipole and the mean polarizability at 632.8 nm and is obtained as (–0.53 ± 0.12)× 10–40 C2 m2 J–1. The principal polarizabilities at 632.8 nm are α11=(5.46 ± 0.14)× 10–40 C2 m2 J–1, α22=(6.69 ± 0.17)× 10–40 C2 m2 J–1 and α33=(5.28 ± 0.13)× 10–40 C2 m2 J–1. The first hyperpolarizability βK contributes –16% of the Kerr constant at 298 K.

Intermolecular potential of carbon dioxide dimer from symmetry-adapted perturbation theory

Abstract: A four-dimensional intermolecular potential energy surface for the carbon dioxide dimer has been computed using the many-body symmetry-adapted perturbation theory (SAPT) and a large 5s3p2d1f basis set including bond functions. The SAPT level applied is approximately equivalent to the supermolecular many-body perturbation theory at the second-order level. An accurate fit to the computed data has been obtained in a form of an angular expansion incorporating the asymptotic coefficients computed ab initio at the level consistent with the applied SAPT theory. A simpler site-site fit has also been developed to facilitate the use of the potential in molecular dynamics and Monte Carlo simulations. The quality of the new potential has been tested by computing the values of the second virial coefficient which agree very well with the experimental data over a wide range of temperatures. Our potential energy surface turns out to be substantially deeper than previous ab initio potentials. The minimum of −484 cm−1 has ...

A comparison of molecular hyperpolarizabilities from gas and liquid phase measurements

Abstract: The first and second hyperpolarizabilities (β and γ) of eight molecules at a fundamental wavelength of 1064 were measured by gas-phase electric-field-induced second-harmonic generation (EFISH), gas-phase hyper-Rayleigh scattering (HRS), and liquid-phase HRS experiments. The EFISH measurements give accurate values of β and γ for these molecules in the gas phase, and the HRS measurements show that the effective β of these molecules in the liquid is enhanced over the gas-phase value by a factor which varies from ≈0.4 to 2.0, over and above the Lorentz local field factors. Combining all of the measurements provides an accurate, absolute determination of the effective β for HRS in the liquid phase. The results for CCl4, suitable as reference standards, are 〈βVV2〉1/2=18.6±0.7 au in the liquid phase and βxyz=20.7±1.6 au in the gas phase. Comparison of measurements between hydrogenated and deuterated molecules indicates that vibrational contributions to β are small.