title: Accurate partition function for acetylene, 12C2H2, and related thermodynamical quantities.
abstract: The internal partition function (Q(int)) of ethyne (acetylene), (12)C(2)H(2), is calculated by explicit summation of the contribution of all individual vibration-rotation energy levels up to 15,000 cm(-1). The corresponding energies are predicted from a global model and constants reproducing within 3σ all 18,415 published vibration-rotation lines in the literature involving vibrational states up to 8900 cm(-1), as produced by Amyay et al. [J. Mol. Spectrosc. 267, 80 (2011)]. Values of Q(int), with distinct calculations for para and ortho species are provided from 1 to 2000 K, in step of 1 K. The total internal partition function at 298.15 K is 104.224387(47) or 416.89755(19), with the nuclear degeneracy spin factors taken as 1/4:3/4 (astronomer convention) or 1:3 (atmospheric convention), respectively, for para:ortho species. The Helmholtz function, Gibbs enthalpy function, entropy, and specific heat at constant pressure are also calculated over the same temperature range. Accuracies as well as the missing contribution of the vinylidene isomer of acetylene in the calculations are discussed.
authors.affiliation: Service de Chimie Quantique et Photophysique, Faculté des Sciences, Université Libre de Bruxelles (U.L.B.), CP 160/09, Av. Roosevelt, 50, B-1050 Bruxelles, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Amyay
authors.forename: A
authors.initials: A
authors.lastname: Fayt
authors.forename: M
authors.initials: M
authors.lastname: Herman