Light-scattering Virial Coefficient Research Articles

Dispersion of the Rayleigh light-scattering virial coefficients and polarisability anisotropy of CO2

ABSTRACTMeasurements are reported of the depolarisation ratio for Rayleigh scattering by CO for gas pressures up to 5.1 MPa at the wavelength 632.8 nm. The first, second and third light-scattering virial coefficients are extracted, and compared with previous measurements in the literature at 514.5 nm and 488.0 nm. The first light-scattering virial coefficient yields the molecular polarisability anisotropy , and extrapolation of the optical-frequency values to zero frequency yields the electronic contribution to the static polarisability anisotropy. Comparison is made with previous determinations for CO. The measured dispersion of the second light-scattering virial coefficient in the visible is compared against calculated theoretical values.

Calculation and measurement of the second light-scattering virial coefficient of (CH3)2O

Measurements are reported of the depolarization ratio of (CH3)2O at vapour pressures up to 0.5 MPa, and the first and second light-scattering virial coefficients are extracted. The molecular-tensor theory of the second light-scattering virial coefficient Bρ for nonlinear molecules is extended to include for the first time those contributions in the scattered intensity arising from field gradient effects and induced quadrupole moments in the molecular interactions. This new theory for Bρ yields a calculated value for (CH3)2O which agrees with the experimental value to within 7%.

Depolarized interaction-induced Rayleigh light scattering in gaseous SO2

The second light-scattering virial coefficient, B ρ, of SO2 has been extracted from measurements of the depolarization ratio ρ at gas pressures up to 1 MPa. The value calculated using our recent molecular-tensor theory of B ρ for nonlinear molecules agrees with the experimental value to within 5%, providing further evidence that a comprehensive dipole—induced-dipole theory of molecular interaction effects explains the observed phenomena adequately

Calculation and measurement of the second light-scattering virial coefficients of nonlinear molecules: a study of ethene

The second light-scattering virial coefficient B ρ of ethene has been extracted from measurements of the depolarization ratio ρ at gas pressures up to 3·2 MPa. The value calculated using our recent molecular tensor theory of B ρ for axially symmetric molecules, underestimates the experimental value by 40%. A complete molecular tensor theory of B ρ for nonlinear molecules is presented, and leads to a calculated value for ethene which is within 2% of the experimental value.

Calculation and measurement of the second light-scattering virial coefficients of nonlinear molecules: a study of ethene

The second light-scattering virial coefficient B ρ of ethene has been extracted from measurements of the depolarization ratio ρ at gas pressures up to 3·2 MPa. The value calculated using our recent molecular tensor theory of B ρ for axially symmetric molecules, underestimates the experimental value by 40%. A complete molecular tensor theory of B ρ for nonlinear molecules is presented, and leads to a calculated value for ethene which is within 2% of the experimental value.

Light Scattering from Associating Polymers in Solution

The effects of polymolecularity on the second and third light-scattering virial coefficients are calculated for some sample distributions and compared to the values obtained from an approximate treatment by Burchard and coworkers. It is concluded that the Burchard scheme, designed to facilitate the evaluation of light scattering data for associating systems, is generally reliable.

Measurement and interpretation of the second light-scattering virial coefficients of linear and quasi-linear molecules

Measurements are reported of the depolarization ratios of CO2, N2, CH3CH3, CH3Cl and CO at gas pressures up to 5·2 MPa, and the first and second light-scattering virial coefficients are extracted. The apparatus and experimental procedures are described briefly. Experimental values of the second light-scattering virial coefficient are compared with calculated theoretical values. For CO2, N2 and CH3Cl the agreement is within 10%, and for CO and CH3CH3 it is within 20%.

Higher-order dipole-dipole, dipole-quadrupole and field gradient contributions to the second light-scattering virial coefficient

Theory of the second light-scattering virial coefficient Bp is extended to include in the scattered intensity terms that have not previously been considered, namely dipole-dipole intensities of the fifth power in the molecular polarizability α as well as additional contributions arising from field gradient effects and induced quadrupole moments in the molecular interactions. Numerical calculations for ten gases show that terms in α5 make a significant contribution to B ρ of up to nearly 20%. In polar molecules, terms in α2 A (where A describes the dipole induced by a field gradient, or the quadrupole induced by a field) make contributions of up to 9%. Indications are that in molecules with a centre of inversion, for which A is zero, field gradient and quadrupole effects will generally lead to contributions of less than 1%.

Calculations of second light-scattering virial coefficients of linear and quasi-linear molecules

The molecular theory of the second light-scattering virial coefficient B ρ is briefly reviewed, and tensor expressions for contributions to B ρ of linear molecules, correct to the fourth power of the polarizability in the depolarized scattered intensity, are presented. These expressions are evaluated numerically by computer for nine gases and, where possible, compared with published experimental values. The results identify molecules which may be fruitfully investigated experimentally. The calculations also demonstrate the usefulness of an algebraic package (in this case Derive) in the accurate performance by computer of tedious manipulations often encountered in the theory of molecular interactions.