0+ States of 8Be

The Law of Corresponding States has been demonstrated for a number of pure substances and binary mixtures, and provides evidence that the transport properties viscosity and diffusion can be determined from a molecular shape function, often taken to be a Lennard-Jones 12-6 potential, that requires two scaling parameters: a well depth ε ij and a collision diameter σ ij , both of which depend on the interacting species i and j. We obtain estimates for ε ij and σ ij of interacting species by finding the values that provide the best fit to viscosity data for binary mixtures, and compare these to calculated parameters using several "combining rules" that have been suggested for determining parameter values for binary collisions from parameter values that describe collisions of like molecules. Different combining rules give different values for σ ij and ε ij and for some mixtures the differences between these values and the best-fit parameter values are rather large.There is a curve in (ε ij, σ ij ) space such that parameter values on the curve generate a calculated viscosity in good agreement with measurements for a pure gas or a binary mixture. The various combining rules produce couples of parameters ε ij , σ ij that lie close to the curve and therefore generate predicted mixture viscosities in satisfactory agreement with experiment. Although the combining rules were found to underpredict the viscosity in most of the cases, Kong's rule was found to work better than the others, but none of the combining rules consistently yields parameter values near the best-fit values, suggesting that improved rules could be developed.Keywords: viscosity, transport properties, combining rules, intermolecular potential parameters 3 I -IntroductionMany important phenomena that occur in gas mixtures depend on molecular transport processes including viscosity, diffusion, and thermal conductivity. Transport properties are often critically important in engineering applications and for understanding phenomena like combustion processes, hypersonic flows, and chemical vapor deposition. A recent trend in engineering design is to use modeling to reduce design times, and combustion is an area benefitting from this approach. Modeling combustion processes requires accurate values of transport properties over a wide range of temperatures and pressures. It is not possible to measure all the requisite transport properties, so we must have models to calculate them. This requires adequate information about the intermolecular potential and the underlying dynamics. The shape function, φ, is frequently taken to be a Lennard-Jones 12-6 potential, where the energy scaling parameter ε ij is the well depth, and σ ij is the length scaling parameter that defines the intermolecular separation at which the potential is zero. Viscosity measurements of a single chemical species allow direct estimation of the parameters that describe the interaction between two molecules of the same species, ε ii and σ ii . The situation is more complicated for even the si...

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“…Kim and Ross [10] and Barker and Pompe [11] found that diffusion coefficients are remarkably insensitive to the intermolecular potential.…”

Section: -Introductionmentioning

confidence: 99%

Intermolecular potential parameters and combining rules determined from viscosity data

Bastien

Price

Brown

2010

Int J of Chemical Kinetics

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“…The shape of this tail is, as the energy increases, determined by the competition between the increasing denominator in the ground-state line shape and (in the numerator) the rapidly increasing penetration factor for the α-α breakup through the Coulomb barrier [38][39][40][41]. This blown-up high-energy tail of the 8 Be ground-state distribution is what is known as the ghost of the 8 Be ground state.…”

Section: Breakup Through the Ghost Of The 8 Be Ground Statementioning

confidence: 99%

Breakup channels forC12triple-αcontinuum states

Diget¹,

Barker²,

Borge³

et al. 2009

Phys. Rev. C

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“…This pleasing combination is attained through use of exponential damping factors. We note that the HFD parameterization is a generalization of the Buckingham-Corner (BC) potential, 10 and is somewhat akin to the BarkerPompe form, 62 both of which were investigated in detail in Paper I. In fitting the potential to their DCS data, Smith et al 15 varied only the r m and f: parameters of the HFD model; they relied on recent theoretically determined dispersion coefficients C 6 , C 8 , and C 10 54 and on repulsion parameters fitted to SCF-HF calculations.…”

Section: Discussionmentioning

confidence: 99%

Scattering of thermal He beams by crossed atomic and molecular beams. II. The He–Ar van der Waals potential

Keilb

Slankas

Kuppermann

1979

The Journal of Chemical Physics

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Differential cross sections for He-Ar scattering at room temperature have been measured. The experimental consistency of these measurements with others performed in different laboratories is demonstrated. Despite this consistency, the present van der Waals well depth of 1.78 meV, accurate to 10%, is smaller by 20% to 50% than the experimental values obtained previously. These discrepancies are caused by differences between the assumed mathematical forms or between the assumed dispersion coefficients of the potentials used in the present paper and those of previous studies. Independent investigations have shown that the previous assumptions are inappropriate for providing accurate potentials from fits to experimental differential cross section data for He-Ar. We use two forms free of this inadequacy in the present analysis: a modified version of the Simons-Parr-Finlan-Dunham (SPFD) potential, and a double Morse-van der Waals (M 2 SV) type of parameterization. The resulting He-Ar potentials are shown to be equal to within experimental error, throughout the range of interatomic distances to which the scattering data are sensitive. The SPFD or M 2 SV potentials are combined with a repulsive potential previously determined exclusively from fits to gas phase bulk properties. The resulting potentials, valid over the extended range of interatomic distances r $ 2.4 A., are able to reproduce all these bulk properties quite well, without adversely affecting the quality of the fits to the DCS.

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0+ States of 8Be

Cited by 54 publications

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Intermolecular potential parameters and combining rules determined from viscosity data

Intermolecular potential parameters and combining rules determined from viscosity data

Breakup channels forC12triple-αcontinuum states

Scattering of thermal He beams by crossed atomic and molecular beams. II. The He–Ar van der Waals potential

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