Improved Partition Functions and Related Thermochemical Quantities for the 16O2 and H216O Molecules

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, 16O2 and H216O, respectively. The new results update those of two previous publications reported in this journal [Furtenbacher et al., J. Phys. Chem. Ref. Data 45, 043104 (2016) and Furtenbacher et al., J. Phys. Chem. Ref. Data 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 International System of Units, (b) an improved set of empirical energy levels for H216O, with much improved uncertainties at low rovibrational excitations, (c) different approaches to the uncertainty budget, including correcting an error in previous uncertainty calculations for 16O2, and (d) a small correction to the ideal-gas thermochemical functions of 16O2, making them applicable for oxygen of natural isotopic composition, which is needed for the development of practical thermodynamic models.