Louis Biolsi

Binary collision dynamics and numerical evaluation of dilute gas transport properties for potentials with multiple extrema

Prediction of gaseous transport properties requires calculation of Chapman–Enskog collision integrals which depend on all possible binary collision trajectories. The interparticle potential is required as input, and for a variety of applications involving monatomic gases the Hulburt–Hirschfelder potential is useful since it is determined entirely from spectroscopic information and can accomodate the long‐range maxima and minima found in many systems. Hulburt–Hirschfelder potentials are classified into five distinct types according to their qualitative binary collision dynamics, which in general can be quite complex and can exhibit ’’double orbiting’’, i.e., a pair of orbiting impact parameters for a single energy of collision. The collision integral program of O’Hara and Smith has been revised extensively to accomodate all physical cases of the Hulburt—Hirschfelder potential, and the required numerical methods are described and justified. The revised program substantially extends the range of potentials f...

Theoretical calculation of the transport properties of monatomic lithium vapor

Transport properties of dilute monatomic gases depend on two body atom–atom interaction potentials. When two ground state (2S) lithium atoms interact, they can follow either of two potential energy curves corresponding to the Li2 molecule in the X 1Σ+g or 3Σ+u state. Transport collision integrals for these states have been calculated by accurately representing quantum mechanical potential energy curves with the Hulburt–Hirschfelder potential. The excellent agreement of calculated viscosities with experimental results provides further evidence that this potential can be used to estimate accurately transport properties under conditions where experimental data are sparse or unavailable.

Calculation of the thermophysical properties of ground state sodium atoms

Transport properties of dilute monatomic gases depend on the two body interaction potentials between the atoms. When two ground state sodium atoms interact, they can follow either of two potential energy curves corresponding to the Na2 molecule in the X 1Σ+g or the 3Σ+u state. Transport collision integrals and second virial coefficients of monatomic sodium have been calculated by accurately representing quantum mechanical potential energy curves with the Hulburt–Hirschfelder potential. The generally good agreement of calculated viscosities and second virial coefficients with the available experimental viscosities and with previously calculated virial coefficients provides further evidence that this approach can be used for accurate estimates of thermophysical properties under conditions where experimental data are sparse or unavailable.

On the Existence of Minima and Maxima in the Composition Dependence of the Thermal Diffusion Factor and Thermal Conductivity

The kinetic theory of nonspherical molecules is shown to be unable to account for sharp dips in the composition dependence of the thermal diffusion factor and thermal conductivity of He–H2 mixtures; at most only shallow minima can be accommodated. No maxima or minima in the thermal diffusion factor of Xe–CO2 can be accounted for. In view of these results and the recent careful measurements on He–H2 by Taylor and Weissman, it is concluded that the anomalies reported previously are probably spurious.

Molecular Collisions. XIII. Nuclear Spin and Statistics Effects for Nearly Spherical Potentials

The effects of nuclear spin on the expressions for the degeneracy averaged cross section for the collision between rigid diatomic molecules with rotational structure which interact through a soft, nearly spherical potential are considered. The development is based on a perturbation method which is essentially an extended distorted wave treatment. Explicit expressions for the moments of the cross section to second order are obtained. Collisions between identical molecules are also considered and the total inelastic cross section is calculated.

Predicting transport properties without adjustable parameters: A test application of the Hulburt-Hirschfelder potential to argon

Abstract Accurate estimates of the transport properties of gaseous systems under conditions where experimental transport data are sparse of unavailable are important in a number of applications. The Hulburt-Hirschfelder (HH) potential for monatomic gas interactions, which is determined entirely by spectroscopic constants of diatomic molecules, provides a basis for calculating transport properties without adjustable parameters. In this paper we report test calculations of the viscosity, thermal conductivity and self-diffusion coefficients for argon. Comparison with the comprehensive correlation of thermophysical properties for argon by Kestin and co-workers shows very reasonable agreement for the transport properties at moderate and high temperatures. Deviations at lower temperatures may be attributed to inaccuracies in the long-range part of the HH potential, whereas the core and well of the potential appear to be adequately represented. These results strongly support the use of the HH potential for estimating the transport properties of monatomic gases at high t

Thermodynamic properties of nitrogen molecules at high temperatures

Calculations of the second virial coefficients and their derivatives for the Hulburt-Hirschfelder (HH) and other accurate interaction potentials are used to determine the thermodynamic properties of nitrogen at high temperatures. Unlike the usual methods employing partition functions, which are most accurate at low temperatures where the energy levels are precisely known, the virial coefficient method depends on integrating over potential energy functions which provide a useful description of energies even near the top of the potential well, a region where the vibrational-rotational energy levels are not readily accessible. This makes this method particularly useful for predicting high-temperature properties outside the range of laboratory measurements and beyond the useful limits of the partition function approach. In the present work, we use the virial coefficient method to predict the heat capacities and enthalpies of nitrogen up to 25,000 K.

Glory Scattering in Molecular Collisions: Formal Expressions for the Total Cross Section

An extended distorted‐wave treatment is used to obtain formal expressions for the total cross section when two rigid diatomic molecules with orbital and nuclear‐spin angular momenta collide. Explicit expressions are obtained through second order, including the lowest‐order inelastic effects.

Effect of molecular angular momentum on the thermal conductivity of a multicomponent gas mixture

The effects of molecular angular momentum (spin polarization) on the thermal conductivity of a multicomponent gas mixture are considered. The Wang Chang–Uhlenbeck approach to the kinetic theory of gases with internal states is used. Formal results are obtained for the thermal conductivity of a gas mixture of uniform composition. These results are given in terms of the quantum mechanical degeneracy‐averaged cross section.

Glory scattering in molecular collisions. III. Collisions between indistinguishable molecules

An extended distorted‐wave treatment is used to obtain formal expressions for the total cross section when two indistinguishable rigid diatomic molecules, with orbital and nuclear spin angular momenta, collide. Explicit expressions for the cross section are obtained through second order, including the lowest order inelastic effects. An expression for the total inelastic cross section is also given. The results are compared with the corresponding results when distinguishable molecules collide.