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Featured researches published by N.D. Hamer.


Chemical Physics Letters | 1978

An efficient microcanonical sampling method

E.S. Severin; B.C. Freasier; N.D. Hamer; D.L. Jolly; Sture Nordholm

Abstract A new microcanonical sampling procedure is presented which incorporates much of the simplicity and efficiency of the canonical procedures. Comparison with previous procedures indicates that the gain in efficiency is substantial. The relevance to numerical simulation of rate processes and equilibrium systems is noted.


Chemical Physics | 1979

Effective vibrational potentials of bromine in argon. Monte Carlo simulation in a mixed ensemble

B.C. Freasier; D.L. Jolly; N.D. Hamer; Sture Nordholm

Abstract We are concerned here with medium effects on the vibrational—rotational properties of a molecule. An efficient Monte Carlo simulation procedure is presented by, which these properties can be studied for a fixed energy of the guest molecule. This is done by extending a recently developed microcanonical sampling method to a mixed ensemble method where the a priori information is partly of a microcanonical and the remainder of a canonical character. The new method is applied to a bromine molecule at high energy in an argon medium at several temperatures and densities. The dependence of the bond length on the medium is illustrated and an effective vibrational potential including medium effects is obtained by a microcanonical inversion procedure.


Chemical Physics | 1986

Theory of collisional energy transfer - bromine in low-density inert gases

B.C. Freasier; D.L. Jolly; N.D. Hamer; Sture Nordholm

Abstract Classical binary collision trajectory calculations have been carried out to study the energy transfer efficiency between the internal degrees of freedom of highly energized bromine (Br 2 ) and the translation degrees of freedom of an inert gas (He, Ne, Ar, Kr, Xe) in the low-density limit. The dependence on species (mass, strength of attraction), temperature of the gas ( T = 160, 300, and 1500 K) and internal energy of the bromine (14, 28, 43 kcal/mole; E d = 45.5 kcal/mole) is considered. Global statistical theories overestimate the average energy transferred per collision by an order of magnitude or more. A simple impulsive collision theory is developed and found to account for the magnitudes (typically within a factor of 2–3) and the gross-trends to reasonable accuracy.


Chemical Physics | 1982

Simulation of relaxation by binary collisions: Comparison with relaxation in a fluid for bromine in argon

D.L. Jolly; B.C. Freasier; N.D. Hamer; Sture Nordholm

Abstract An efficient computer algorithm for the sampling and calculation of binary-collision trajectories has been developed and applied to the study of the relaxation of highly energized bromine in argon. The dependence of energy and angular-momentum transfer and rotational—vibrational redistribution upon temperature and impact parameter is investigated. The results for total transfer rates are compared with previous results obtained by Monte Carlo/molecular dynamics simulation of the corresponding fluid at various densities. Significant deviations between the predictions of binary-collisions and fluid simulations are found and interpreted in terms of local heating of the fluid.


Chemical Physics | 1980

Theory of solvent effects on the equilibrium properties of a diatomic guest molecule

Sture Nordholm; B.C. Freasier; N.D. Hamer; D.L. Hamer; D.L. Jolly

Abstract The medium effects on the equilibrium properties of a diatomic molecule in a simple fluid medium have been simulated using a mixed ensemble Monte Carlo method in the special case of bromine in argon. The change in the bond length distribution has been obtained over a range of densities and temperatures of the medium. A statistical theory based on a treatment of the medium as a van der Waals fluid is developed and used to predict the apparent change in the vibrational potential due to the medium. Good agreement is obtained between theory and simulation for low to moderate fluid densities but the effects are overestimated for highly dense fluids.


Molecular Physics | 1979

Dielectric properties of a mixture of dipolar hard spheres

B.C. Freasier; N.D. Hamer; Dennis J. Isbister

A theory for the dielectric constant, e, of a fluid mixture of dipolar hard spheres is formulated by generalizing the methods developed by Ramshaw and Wertheim for the pure fluid case. The resulting expression for e depends on the pair distribution functions, g αβ(r 1, θ1, r 2, θ2) for a dipolar mixture. Due to the unavailability of exact representations for these dipolar pair distribution functions, the results of the mean spherical approximation are employed in the formalism developed. Numerical results are given for e as calculated from the pair distribution functions for a spherical volume of macroscopic dimensions. The compositional dependence of the e obtained in this way for a specific mixture is compared with the corresponding properties of the well established theories of Clausius-Mossotti-Debye and Onsager. In addition, the relative importance of the dipole moment and size of the hard sphere parameters in determining e for a dipolar mixture (the correlative behaviour of which is described by the...


Chemical Physics | 1981

Density effects in collision induced light absorption in helium-argon mixtures

B.C. Freasier; N.D. Hamer

Abstract Density corrected distribution functions are used to calculate γ o and γ 2 moments for the collision induced absorption spectra of a helium-argon system for a number of assumed dipole moment functions. These calculations indicate that corrections due to density effects can be of greater magnitude than the quantum corrections for these moments and can account for 10% of the moment at 200 amagats. The density corrections for γ o show great variability with the choice of dipole parameters while the corrections for ν 2 were very consistent irrespective of the precise values of the dipole parameters. In addition, we correct some errors in our previous paper on the formal theory of these moments.


Chemical Physics | 1977

Density effects in collision induced light absorption of inert gas mixtures

N.D. Hamer; B.C. Freasier; Richard J. Bearman

Abstract A general density expansion formalism is derived for the first two non-zero classical moments of the collision induced light absorption spectrum for inert gas mixtures. This formalism is reduced to numerically tractable expressions for the first higher order density corrections.


Chemical Physics | 1984

Bromine-bromine energy transfer by binary collisions

D.L. Jolly; B.C. Freasier; N.D. Hamer; Sture Nordholm

Abstract The collisional energy transfer between a highly excited bromine molecule and a non-reactive monatomic (Ar or Br) or diatomic (Br 2 ) medium has been investigated by binary trajectory calculations over a wide range of medium temperatures and internal energies of the reactant molecule. The efficiency of the energy transfer is compared with expectations based on simple statistical approximations used in unimolecular reaction rate theory. Large deviations are found, particularly with respect to the contributions made by different types of degrees of freedom and to the dependence on the internal energy of the reactant molecule. Transfer to or from vibrational degrees of freedom appears to be very inefficient. Translational energy is most readily transferred. The rate coefficient for energy transfer appears to decrease with increasing internal energy in most cases.


Journal of Chemical Physics | 1981

Existence of the dielectric constant in dipolar fluid mixtures

John D. Ramshaw; N.D. Hamer

The existence of the dielectric constant e is investigated for fluid mixtures of rigid polar molecules. The investigation is performed using the functional‐derivative formalism for mixtures, and is closely analogous to that previously carried out for pure dipolar fluids [J. Chem. Phys. 68, 5199 (1978)]. Sufficient conditions for the existence of e are obtained in terms of the direct correlation function matrix cαβ(12). It is found that e exists if cαβ(12) depends only on relative positions and orientations, and becomes asymptotic to −ϑαβ(12)/kT at long range, where ϑαβ(12) is the dipole–dipole potential between a molecule of species α and one of species β. An expression for e in terms of the short‐range total correlation function matrix emerges automatically from the development. This expression is equivalent to an earlier result obtained by a different method. Expressions for e in terms of cαβ(12) are derived for axially symmetric molecules and for molecules of arbitrary symmetry. In the former case, the...

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B.C. Freasier

University of New South Wales

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D.L. Jolly

University of New South Wales

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John D. Ramshaw

Los Alamos National Laboratory

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D.L. Hamer

University of New South Wales

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Dennis J. Isbister

University of New South Wales

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E.S. Severin

University of New South Wales

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Richard J. Bearman

University of New South Wales

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