Active Thermochemical Tables: A Revision of the Enthalpy of Formation of Gas-Phase Sulfur Atom and a Refinement of the Thermochemistry of Several Other Key Sulfur Species

Abstract Using the Active Thermochemical Tables (ATcT) approach, the 298.15 K standard enthalpy of formation of sulfur atom has been revised to 279.10 ± 0.12 kJ mol–1 (276.85 ± 0.12 kJ mol–1 at 0 K). The new ATcT value is nearly 2 kJ mol–1 higher than the original CODATA recommendation, with the difference being an order of magnitude larger than the combined uncertainties of the two. The CODATA value critically depends on pairing the bond dissociation energy of gas-phase S2 with its enthalpy of formation. Early ATcT analyses involving a localized thermochemical network (TN) have strongly suggested that the observed predissociations from the B 3Σu– state of S2(g) and B 3Σ– state of SO(g) both refer to the ground-state limit, S (3P2) + S (3P2) and S (3P2) + O (3P2), respectively, rather than the excited S (3P2) + S (3P1) limit in S2(g), as originally assumed by [ Ricks, J. M.; Barrow, R. F.Can. J. Phys.1969, 47, 2423–2427. 10.1139/p69-297]. and accepted by CODATA, or the S (3P2) + O (3P1) limit in SO(g), as assumed by [ Clerbaux, C.; Colin, R.J. Mol. Spectrosc.1994, 165, 334–348. 10.1006/jmsp.1994.1137].. For S2(g), this was later experimentally confirmed by [ Frederix, P. W. J. M.; et al.J. Phys. Chem. A2009, 113, 14995–15005. 10.1021/jp905104u].. The ATcT analyses also suggested that the CODATA enthalpy of formation of gas-phase S2 is much less robust than initially assumed. In contrast to the CODATA single-path provenance of the enthalpy of formation of sulfur atom, the distributed provenance of the ATcT value, which takes into account the sequential bond dissociation energies of SO2(g) and H2S(g), as well as thermochemical cycles involving sulfuric acid, suggests that the ATcT value is quite robust. The new enthalpy of formation of sulfur atom affects, inter alia, all electronic structure computations that rely on converting the theoretical total atomization energies to enthalpies of formation. In addition to providing a revised value for the enthalpy of formation of sulfur atom, ATcT also produces revised and improved enthalpies of formation for nearly 200 sulfur-containing chemical species.