Thermodynamic Properties of Gaseous Ruthenium Species

Abstract

The review of thermodynamic data of ruthenium oxides reveals large uncertainties in some of the standard enthalpies of formation, motivating the use of high-level relativistic correlated quantum chemical methods to reduce the level of discrepancies. The reaction energies leading to the formation of ruthenium oxides RuO, RuO2, RuO3, and RuO4 have been calculated for a series of reactions. The combination of different quantum chemical methods has been investigated [DFT, CASSCF, MRCI, CASPT2, CCSD(T)] in order to predict the geometrical parameters, the energetics including electronic correlation and spin-orbit coupling. The most suitable method for ruthenium compounds is the use of TPSSh-5%HF for geometry optimization, followed by CCSD(T) with complete basis set (CBS) extrapolations for the calculation of the total electronic energies. SO-CASSCF seems to be accurate enough to estimate spin-orbit coupling contributions to the ground-state electronic energies. This methodology yields very accurate standard enthalpies of formations of all species, which are either in excellent agreement with the most reliable experimental data or provide an improved estimate for the others. These new data will be implemented in the thermodynamical databases that are used by the ASTEC code (accident source term evaluation code) to build models of ruthenium chemistry behavior in severe nuclear accident conditions. The paper also discusses the nature of the chemical bonds both from molecular orbital and topological view points.

Gaseous phase above Ru–O system: A thermodynamic data assessment

“…Indeed, those measured in the presence of Ne are discarded because they might be influenced by Van Der Vaals interactions in the case of this rare gas with higher molar mass. The ab-initio frequency set calculated by Hameka et al [5] and Miradji et al [7] confirms the present experimental selection while being slightly higher in relation with an interatomic Ru-O distance calculated shorter than from our selected experimental values. The selected ground electronic state is the one calculated by Miradji et al [7] 1 A 1 with a triplet state at an electronic level 14210 cm -1 (1.76 eV).…”

“…Interatomic Ru-O distances in the gaseous molecules as well as methods of measurement and / or calculations come from Hameka et al [5], Siegbahn [6] , Miradji et al [7], Zhou et al [8], Krauss et Stevens [9], Schäfer et al [10] and Scullman and Thelin [12]. Distances in the two varieties of RuO 4 (s) solid crystal published by Pley and Wickleder [11] are considered (see Table 1 in Appendix I).…”

High-resolution infrared spectroscopy and analysis of the ν2/ν4 bending dyad of ruthenium tetroxide

“…It is a first step on the way to a more precise structural parameters of this important benchmark molecule. This molecule poses also many challenging questions to ab initio quantum chemical calculations, as a recent study points out [14]. Among other properties, the predicted bond length varies substantially from one method to the next and is calculated always shorter.…”

“…For this reason, the possible remote sensing of this compound in the atmosphere has gained technological importance and motivated recent spectroscopic studies [7]. Besides this interest motivated by nuclear reactor technology, detailed studies of RuO 4 high resolution FTIR absorption spectrum present an interest for quantum chemistry, as it would provide vibrational and structural parameters as benchmarks for the modeling of heavy element compounds [8][9][10][11][12][13][14].…”

“…These have, from band shape studies and force fields, approximately estimated band center positions, as well as rotational and Coriolis constants. These studies have been used ever since as benchmarks for ab initio calculations of vibrational properties [11][12][13][14].…”