Calculation of thermophysical properties of nitrogen gas based on an ab initio intermolecular potential energy surface

R. Hellmann1, E. Bich1 and E. Vogel1

1Institute of Chemistry, University of Rostock, Rostock, Germany

Keywords: ab initio calculations
property: virial coefficients, transport properties
material: nitrogen

Advances in computer technology make it possible to determine the thermophysical properties of gases with high accuracy entirely from theory. For very low and very high temperatures and also for highly corrosive or toxic substances, ab initio computations represent a reasonable alternative to experiments to obtain accurate values for thermophysical properties.

The kinetic theory of gases can be utilized to predict the transport and relaxation properties of a gas directly from its intermolecular potential energy surface [1]. Based on a classical mechanical description of the intermolecular collision process, transport and relaxation properties of important gases such as methane [2,3], water vapor [4], and hydrogen sulfide [5] have already been computed in recent years. In most cases the deviations from the best experimental data were smaller than 1% for viscosity and thermal conductivity.

Nitrogen gas is very important as a reference fluid and its thermophysical properties are very accurately known from experiments at temperatures not too far away from ambient temperature. However, at higher temperatures the reliability of the experimental data decreases generally, whereas for such conditions thermophysical properties computed from theory retain their accuracy. Therefore, we have computed an intermolecular potential energy surface for two nitrogen molecules based on high-level quantum-mechanical ab initio methods. Results for viscosity and thermal conductivity as well as for the second and third pressure virial coefficients will be presented. The uncertainties of the calculated values for the transport properties are estimated to be less than 0.5% for temperatures up to 2000 K.

  1. A.S. Dickinson, R. Hellmann, E. Bich, E. Vogel, Phys. Chem. Chem. Phys. 9, 2836 (2007)

  2. R. Hellmann, E. Bich, E. Vogel, A.S. Dickinson, V. Vesovic, J. Chem. Phys. 129, 064302 (2008)

  3. R. Hellmann, E. Bich, E. Vogel, A.S. Dickinson, V. Vesovic, J. Chem. Phys. 130, 124309 (2009)

  4. R. Hellmann, E. Bich, E. Vogel, A.S. Dickinson, V. Vesovic, J. Chem. Phys. 131, 014303 (2009)

  5. R. Hellmann, E. Bich, E. Vogel, V. Vesovic, in preparation

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