About isotope equilibrium between liquid and vapour phases†

^†Revised version of a paper presented at the 9th. Symposium of the European Society for Isotope Research (ESIR), 23 to 28 June, Cluj-Napoca, Romania.

Abstract

A new semi-empirical formula was devised for liquid–vapour fractionation at thermodynamic equilibrium, which is valid for the whole temperature range, i.e. from the freezing to the critical temperature, T _c. The new formula contains three parameters (A, B and C) only:

where X is the ratio of saturated vapour pressure at temperature T to the critical pressure. Physical reasons for the above formula are presented. The following numerical values of the parameters have been obtained by fitting the above expression to the experimental data from literature: A=1.3781×10⁶, B=1.8876×10³, C=3655.8 for ¹⁸O/¹⁶O, and A=18.993×10⁶, B=40.798×10³, C=18405 for D/H isotope fractionation. In both cases, X was calculated from the Van der Waals semi-empirical formula for vapour pressure, which has only one crude parameter:

^†Revised version of a paper presented at the 9th. Symposium of the European Society for Isotope Research (ESIR), 23 to 28 June, Cluj-Napoca, Romania.

Keywords:

• hydrogen-2
• isotope fractionation
• model
• oxygen-18
• surface tension
• vapour pressure
• water

Acknowledgements

Thanks are due to Mr. Zenon Dmitruk from the Institute of Physics and to my student, Mr. Łukasz Gajownik, for their help in preparation of the presentation. I am grateful to Dr. Tomasz Pieñkos for his assistance in calculation of the constants A, B and C for oxygen and hydrogen isotope fractionation. Those values were calculated by use of the CurveExpert program. The constructive comments by two unknown reviewers increased the understanding and overall quality of the paper.

Notes

^†Revised version of a paper presented at the 9th. Symposium of the European Society for Isotope Research (ESIR), 23 to 28 June, Cluj-Napoca, Romania.

Additional information

Notes on contributors

Stanislaw Halas

*Email: [email protected]