Abstract: The fractionation of isotopes of natural Ar near the condensation and freezing points was studied using mass spectrometry, numerical modeling, and density functional theory (DFT). Cooling of gaseous Ar to a temperature close to the boiling point leads to separation coefficients α40 = 0.59, α38 = 1.95, and α36 = 1.66 for 40Ar, 38Ar, and 36Ar, respectively, which is probably due to the formation of 40Ar2 dimers and their retention in the cryostat. DFT calculations indicate attraction between Ar atoms, and therefore the preferred state of Ar is determined by the number of nearest neighbors. As a result, dimers are destroyed in the liquid phase, and separation decreases (α40 = 0.98, α38 = 1.06 and α36 = 1.01), but remains high compared to kinetic fractionation due to the difference of ~50 J/mol between the heat of condensation of 40Ar and the dissolution of 38Ar and 36Ar in the condensate. The formation of the solid phase occurs with the predominant freezing of the heaviest isotope 40Ar for kinetic reasons (α40 = 1.02, α38 = 0.98 and α36 = 0.98).

Cite: Cholach A.R.
Fractionation of Isotopes in Moderately Cooled Argon
Separation and Purification Technology. 2025. V.377. NPart A. 134232 :1-8. DOI: 10.1016/j.seppur.2025.134232 OpenAlex

Dates:

Submitted:	Apr 10, 2025
Accepted:	Jul 4, 2025
Published online:	Jul 6, 2025
Published print:	Dec 19, 2025

Identifiers:

OpenAlex:

W4412064375

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