Furtenbacher, T; Szidarovszky, T; Hruby, J; Kyuberis, AA; Zobov, NF; Polyansky, OL; Tennyson, J; Furtenbacher, T; Szidarovszky, T; Hruby, J; Kyuberis, AA; Zobov, NF; Polyansky, OL; Tennyson, J; Császár, AG; - view fewer (2016) Definitive Ideal-Gas Thermochemical Functions of the H216O Molecule. Journal of Physical and Chemical Reference Data , 45 (4) , Article 043104. 10.1063/1.4967723.

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Abstract

A much improved temperature-dependent ideal-gas internal partition function, Qint(T), of the H216O molecule is reported for temperatures between 0 and 6000 K. Determination of Qint(T) is principally based on the direct summation technique involving all accurate experimental energy levels known for H216O (almost 20 000 rovibrational energies including an almost complete list up to a relative energy of 7500 cm−1), augmented with a less accurate but complete list of first-principles computed rovibrational energy levels up to the first dissociation limit, about 41 000 cm−1 (the latter list includes close to one million bound rovibrational energy levels up to J = 69, where J is the rotational quantum number). Partition functions are developed for ortho- and para-H216O as well as for their equilibrium mixture. Unbound rovibrational states of H216O above the first dissociation limit are considered using an approximate model treatment. The effect of the excited electronic states on the thermochemical functions is neglected, as their contribution to the thermochemical functions is negligible even at the highest temperatures considered. Based on the high-accuracy Qint(T) and its first two moments, definitive results, in 1 K increments, are obtained for the following thermochemical functions: Gibbs energy, enthalpy, entropy, and isobaric heat capacity. Reliable uncertainties (approximately two standard deviations) are estimated as a function of temperature for each quantity determined. These uncertainties emphasize that the present results are the most accurate ideal-gas thermochemical functions ever produced for H216O. It is recommended that the new value determined for the standard molar enthalpy increment at 298.15 K, 9.904 04 ± 0.000 01 kJ mol−1, should replace the old CODATA datum, 9.905 ± 0.005 kJ mol−1.

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