^{1}, George C. McBane

^{2,a)}, Frederick R. W. McCourt

^{3}and William J. Meath

^{4}

### Abstract

Four potential energy surfaces are of current interest for the Ne–CO interaction. Two are high-level fully *ab initio*surfaces obtained a decade ago using symmetry-adapted perturbation theory and supermolecule coupled-cluster methods. The other two are very recent exchange-Coulomb (XC) model potential energy surfaces constructed by using *ab initio* Heitler–London interaction energies and literature long range dispersion and induction energies, followed by the determination of a small number of adjustable parameters to reproduce a selected subset of pure rotational transition frequencies for the van der Waals cluster. Testing of the four potential energy surfaces against a wide range of available experimental microwave, millimeter-wave, and mid-infrared Ne–CO transition frequencies indicated that the XC potential energy surfaces gave results that were generally far superior to the earlier fully *ab initio*surfaces. In this paper, two XC model surfaces and the two fully *ab initio*surfaces are tested for their abilities to reproduce experiment for a wide range of nonspectroscopic Ne–CO gas mixture properties. The properties considered here are relative integral cross sections and the angle dependence of rotational state-to-state differential cross sections, rotational relaxation rate constants for in Ne–CO mixtures at , pressure broadening of two pure rotational lines and of the rovibrational lines in the CO fundamental and first overtone transitions at 300 K, and the temperature and, where appropriate, mole fraction dependencies of the interaction second virial coefficient, the binary diffusion coefficient, the interaction viscosity, the mixture shear viscosity and thermal conductivity coefficients, and the thermal diffusion factor. The XC model potential energy surfaces give results that lie within or very nearly within the experimental uncertainties for all properties considered, while the coupled-cluster *ab initio*surface gives results that agree similarly well for all but one of the properties considered. When the present comparisons are combined with the ability to give accurate spectroscopic transition frequencies for the Ne–CO van der Waals complex, only the XC potential energy surfaces give results that agree well with all extant experimental data for the Ne–CO interaction.

W.J.M. and F.R.W.M. are grateful to NSERC of Canada for the award of Discovery Grants that have funded this research in part.

I. INTRODUCTION

II. THE XC(FIT) MODEL POTENTIAL ENERGY SURFACES

III. MICROSCOPIC PHENOMENA

A. Molecular beam state-to-state differential scattering cross sections

B. State-to-state integral scattering cross sections

IV. MACROSCOPIC PHENOMENA

A. The interaction second virial coefficient

B. Pressure broadening

1. Pure rotational transitions

2. Rovibrational transitions

C. Rotational relaxation

D. Transport properties

1. The binary diffusion coefficient

2. The interaction and mixture shear viscosity coefficients

3. The mixture thermal conductivity coefficient

4. The thermal diffusion factor

V. GENERAL DISCUSSION

### Key Topics

- Thermal diffusion
- 33.0
- Diffusion
- 30.0
- Shear rate dependent viscosity
- 30.0
- Thermal conductivity
- 19.0
- Potential energy surfaces
- 13.0

## Figures

Angular dependence of the location of the repulsive wall corresponding to the turning point in the center-of-mass system for an elastic binary collision between Ne and CO at total relative energies : results are shown for the XC(fit), S2, and SAPT PESs.

Angular dependence of the location of the repulsive wall corresponding to the turning point in the center-of-mass system for an elastic binary collision between Ne and CO at total relative energies : results are shown for the XC(fit), S2, and SAPT PESs.

State-to-state differential cross sections for scattering for an average collision energy of for three PESs and experimental results from Ref. 20. In each panel, the experimental results have been scaled vertically to match the average integral cross section computed from the three surfaces. The calculated curves are identified as in Fig. 1.

State-to-state differential cross sections for scattering for an average collision energy of for three PESs and experimental results from Ref. 20. In each panel, the experimental results have been scaled vertically to match the average integral cross section computed from the three surfaces. The calculated curves are identified as in Fig. 1.

State-to-state relative product densities at 711 and for S2 and surfaces and experimental results from Ref. 19. The vertical scale is arbitrary but corresponds roughly to cross sections in computed on S2.

State-to-state relative product densities at 711 and for S2 and surfaces and experimental results from Ref. 19. The vertical scale is arbitrary but corresponds roughly to cross sections in computed on S2.

Bottom panel: integral cross sections for transitions at for three PESs. The points from each surface are connected by lines to make it easier to follow the patterns. Top panel: density-to-flux factors computed for the PES at , in which is the relative speed of the colliders, is the final laboratory-frame speed of the scattered molecule, and the angular brackets indicate a weighted average over the scattering angle in which the differential cross section is employed as the weighting function.

Bottom panel: integral cross sections for transitions at for three PESs. The points from each surface are connected by lines to make it easier to follow the patterns. Top panel: density-to-flux factors computed for the PES at , in which is the relative speed of the colliders, is the final laboratory-frame speed of the scattered molecule, and the angular brackets indicate a weighted average over the scattering angle in which the differential cross section is employed as the weighting function.

Computed pressure broadening coefficients and experimental results for IR fundamental and overtone lines. Experimental data for the 2-0 band are from Ref. 23. Data for the 1-0 band are from Ref. 24, except for the single point at from Ref. 51. Points labeled “inelastic” were determined with Eq. (5). Points labeled “approx S-G” were determined with Eq. (6).

Computed pressure broadening coefficients and experimental results for IR fundamental and overtone lines. Experimental data for the 2-0 band are from Ref. 23. Data for the 1-0 band are from Ref. 24, except for the single point at from Ref. 51. Points labeled “inelastic” were determined with Eq. (5). Points labeled “approx S-G” were determined with Eq. (6).

## Tables

Temperature dependence of the interaction second virial coefficient for Ne–CO mixtures.

Temperature dependence of the interaction second virial coefficient for Ne–CO mixtures.

Measured and computed pressure broadening coefficients for pure rotational transitions. All coefficients are given in units of . Experimental data are from Ref. 21 for the line and from Ref. 22 for the line.

Measured and computed pressure broadening coefficients for pure rotational transitions. All coefficients are given in units of . Experimental data are from Ref. 21 for the line and from Ref. 22 for the line.

Comparison of calculated and experimental values for the binary diffusion coefficient of Ne–CO mixtures. The first row associated with each temperature gives the CT values for the diffusion coefficient; the second row gives the corresponding MM value.

Comparison of calculated and experimental values for the binary diffusion coefficient of Ne–CO mixtures. The first row associated with each temperature gives the CT values for the diffusion coefficient; the second row gives the corresponding MM value.

Comparison of calculated and experimental interaction shear viscosity values for Ne–CO binary mixtures. The upper row at each temperature gives CT values while the lower row gives MM approximation values for . The final column gives values of extracted from the data of Ref. 29.

Comparison of calculated and experimental interaction shear viscosity values for Ne–CO binary mixtures. The upper row at each temperature gives CT values while the lower row gives MM approximation values for . The final column gives values of extracted from the data of Ref. 29.

Comparison between calculated and experimental values of the mixture shear viscosity (units in ). The first row associated with each pair contains results obtained using the PES, the second row contains results obtained using the S2 PES, and the third row contains results obtained using the SAPT PES. is given by .

Comparison between calculated and experimental values of the mixture shear viscosity (units in ). The first row associated with each pair contains results obtained using the PES, the second row contains results obtained using the S2 PES, and the third row contains results obtained using the SAPT PES. is given by .

Comparison between calculated and experimental mixture thermal conductivities for Ne–CO mixtures at (units: ).

Comparison between calculated and experimental mixture thermal conductivities for Ne–CO mixtures at (units: ).

Thermal diffusion factor for Ne–CO mixtures at temperature . The experimental results are from Ref. 28.

Thermal diffusion factor for Ne–CO mixtures at temperature . The experimental results are from Ref. 28.

Relative behaviors of the four PESs in predicting thermal diffusion including the average absolute deviations (AAD) between calculated and experimental results.

Relative behaviors of the four PESs in predicting thermal diffusion including the average absolute deviations (AAD) between calculated and experimental results.

A summary of the predictive abilities of various Ne–CO PESs; see Secs. III and IV for details.

A summary of the predictive abilities of various Ne–CO PESs; see Secs. III and IV for details.

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