Second Virial Coefficient of CH4 Vapor in 5 mK-10000 K Temperature Range in Quantum and Classical Regimes

O. Al-Obeidat Department of Physics and Basic Sciences, Faculty of Engineering Technology, Al-Balqa Applied University, Amman, Jordan

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The aim of this work is to study the second virial coefficient B of methane (CH4) vapor over a wide temperature range, T=5 mK-10000 K. The coefficient is calculated in two temperature regions. First, for T=5 mK-20 K - the quantum second virial coefficient Bq is determined for the first time. It is found that the behavior of Bq is similar to that of the CH4-CH4 potential. Standard expressions are then used in this quantum regime at the number density n=1×10-4 Å-3 to compute other thermodynamic properties of the system, i.e., the Helmholtz free energy per molecule, the internal energy per molecule, the entropy per molecule and the specific heat capacity. Second, for T=20-10000 K - the classical second virial coefficient Bcl, the Boyle temperature TB and the inversion temperature Ti are determined. The first quantum correction Bqc is calculated over the temperature range T=20-100 K. It turns out that it is necessary to make such a quantum correction to Bcl for T=20-60 K, whereas the quantum effects are relatively insignificant for T>60 K. In general, our results are in very good agreement with previous theoretical and experimental results.

DOI:10.12693/APhysPolA.139.102 topics: methane (CH4) vapor, second virial coefficient, quantum corrections, quantum regime