Improved Partition Functions and Related Thermochemical Quantities for the (16)O2 and H2(16)O Molecules

Published

July 10, 2025

Author(s)

Tibor Furtenbacher, Allan Harvey, Attila G Császár

Abstract

Based on the direct summation technique, improved ideal-gas partition functions and related thermochemical quantities are reported for the parent isotopologues of molecular oxygen and water, (16)O2 and H2(16)O, respectively. The new results update those of two previous publications reported in this journal [J. Phys. Chem. Ref. Data 45, 043104 (2016) and 48, 023101 (2019)]. The improved thermochemical functions, tabulated at 1 K intervals between 0 and 5000 K in the Supplementary Material to this paper, use (a) the exact values of the fundamental physical constants fixed in the 2019 redefinition of the SI, (b) an improved set of empirical energy levels for H2(16)O, with much improved uncertainties at low rovibrational excitations, (c) different approaches to the uncertainty budget, including correcting an error in previous uncertainty calculations for 16}O2, and (d) a small correction to the ideal-gas heat capacity of (16)O2, making it applicable for oxygen of natural isotopic composition, which is needed for the development of practical thermodynamic models.

Citation

J. Phys. & Chem. Ref. Data (JPCRD) -

Volume

54

Issue

3

NIST Pub Series

J. Phys. & Chem. Ref. Data (JPCRD)

Pub Type

NIST Pubs

Download Paper

https://doi.org/10.1063/5.0273661

Local Download

Keywords

enthalpy, entropy, heat capacity, ideal gas, oxygen, partition function, thermochemistry, water

Citation

Furtenbacher, T. , Harvey, A. and Császár, A. (2025), Improved Partition Functions and Related Thermochemical Quantities for the (16)O2 and H2(16)O Molecules, J. Phys. & Chem. Ref. Data (JPCRD), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.1063/5.0273661, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959474 (Accessed July 12, 2025)