Ab initiopotential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. II. Thermophysical standard values for low-density helium

Abstract

To cite this version:Eckhard Vogel, Eckard Bich, Robert Hellmann. Ab initio potential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. II. Thermophysical standard values for low-density helium. Molecular Physics, Taylor & Francis, 2007, 105 (23-24) A helium-helium interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation considering relativistic retardation effects (R. Hellmann, E. Bich, and E. Vogel, Mol. Phys. (submitted)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body and three-body interactions. The second pressure virial coefficient as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for 3 He and 4 He from 1 K to 10,000 K and the third pressure virial coefficient for 4 He from 20 K to 10,000 K. The transport property values can be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of ±0.02% for temperatures above 15 K. This uncertainty is superior to the best experimental measurements at ambient temperature.

Optimizing acoustic measurements of the Boltzmann constant

“…The most accurate, zero-pressure values of the thermal conductivity of helium are those calculated ab initio from quantum mechanics and statistical mechanics. [17,18]. In the limit of zero density at T TPW , the most accurate value of the thermal conductivity of argon λ Ar is obtained by combining the calculated value of the Prandtl number Pr ≡C p η/λ , the calculated value of the viscosity of helium η He , and the measurements by May et al of the ratio η Ar /η He ≡ (viscosity of argon)/(viscosity of helium).…”

Ab initiopair potential energy curve for the argon atom pair and thermophysical properties of the dilute argon gas. I. Argon–argon interatomic potential and rovibrational spectra

“…The resulting thermophysical properties [3,4] were found to be more accurate than experimental values and can therefore be utilized for calibration of high precision measuring instruments. Since argon is one of the pioneer substances of molecular modeling and a low price alternative for calibration issues, a pair potential of high quality is needed.…”

Accurate potential energy curve for helium dimer retrieved from viscosity coefficient data at very low temperatures

“…For the temperature range required to refine the potential curve between 3 and 4Å, that is, below 5 K, the reference of Becker et al [17] presents 11 values. However, the quality of these data has been questioned [18] due to the use of an old reference value for equipment calibration, resulting in a positive deviation of approximately 5 % as estimated by Bich and Vogel. [18] To generate the necessary data of viscosity coefficients, the equation…”

“…However, the quality of these data has been questioned [18] due to the use of an old reference value for equipment calibration, resulting in a positive deviation of approximately 5 % as estimated by Bich and Vogel. [18] To generate the necessary data of viscosity coefficients, the equation…”