Active Thermochemical Tables: Enthalpies of Formation of Bromo- and Iodo-Methanes, Ethenes and Ethynes

Abstract

The thermochemistry of halocarbon species containing iodine and bromine is examined through an extensive interplay between new Feller−Peterson− Dixon (FPD) style composite methods and a detailed analysis of all available experimental and theoretical determinations using the thermochemical network that underlies the Active Thermochemical Tables (ATcT). From the computational viewpoint, a slower convergence of the components of composite thermochemistry methods is observed relative to species that solely contain first row elements, leading to a higher computational expense for achieving comparable levels of accuracy. Potential systematic sources of computational uncertainty are investigated, and, not surprisingly, spin-orbit coupling is found to be a critical component, particularly for iodine containing molecular species. The ATcT analysis of available experimental and theoretical determinations indicates that prior theoretical determinations have significantly larger uncertainties than originally reported, particularly in cases where molecular spin-orbit effects were ignored. Accurate and reliable heats of formation are reported for 38 halogen containing systems, based on combining the current computations with previous experimental and theoretical work via the ATcT approach.

High-Accuracy Heats of Formation for Alkane Oxidation: From Small to Large via the Automated CBH-ANL Method

“…Perhaps the large uncertainties in the ATcT analysis for the larger species leads to too small a constraint on the consistency between CH 4 and C 2 H 6 . We here also note that recently updated ATcT reference enthalpies used in the present analysis, like that for ethane (−16.35 ± 0.03 kcal mol –1 from version 1.124), lead to significantly more consistent results in Table than those from previous versions ( e.g. , −16.28 ± 0.04 kcal mol –1 for ethane from version 1.118) .…”

“…We here also note that recently updated ATcT reference enthalpies used in the present analysis, like that for ethane (−16.35 ± 0.03 kcal mol −1 from version 1.124), 53 lead to significantly more consistent results in Table 6 than those from previous versions (e.g., −16.28 ± 0.04 kcal mol −1 for ethane from version 1.118). 54 Changes of 0.07 kcal mol −1 to a reference species that is used as frequently as ethane can make large impacts on ΔH f (0 K) values of larger species. Through this observation we see unique potential in the CBH2 schemes, in that the deviation of CBH2 ΔH f (0 K) values in large species may be used to retroactively improve even smallspecies data.…”

Bond Energies of UO+ and UC+: Guided Ion Beam and Quantum Chemical Studies of the Reactions of Uranium Cation with O2 and CO

“…Previous theoretical studies predicted a 4 I 9/2 (σ 2 π 4 [πδϕ]) ground state for UO + (where σ and π are the covalent bonds and the square brackets indicate 5 f electrons) arising primarily from 5f 3 type configurations by a ligand field theory (LFT) calculation, [8] a valence configuration interaction study, [9–10] and ab initio calculations using a cc‐pVTZ basis set [11] . Ground states of both U ( 5f 3 6d 1 7s 2 ) and U + ( 5f 3 7s 2 ) have three electrons in 5 f orbitals, which behave as core orbitals in UH, [12–14] UH + , [12,15] UX 0/+ (X=F, Cl), [16–18] and UO 0/+ molecules [11,19] . This property means that these configurations can be compared directly to transition metal systems and analogous Th species.…”

Refining the thermochemical properties of CF, SiF, and their cations by combining photoelectron spectroscopy, quantum chemical calculations, and the Active Thermochemical Tables approach

“…Since then, the underlying ATcT TN has been successively expanded to fulfil the needs of subsequent studies, such as those involving enthalpies of formation of key bromo- and iodo-methanes, ethenes and ethynes, 93 the ring-opening dynamics of cyclopropyl and cyclopropylium (ATcT TN versions 1.128 and 1.130), 94 the bond dissociation energy and the adiabatic ionisation energy of CH (ATcT TN ver. 1.140), 62 the role of methanediol in the atmosphere (ATcT ver.…”

“…1.124), 39 which contains nearly 2800 chemical species, has been developed within the context of several studies, such as the report on thermophysical and thermochemical properties of CH 2 and CH 3 using nonrigid rotor anharmonic oscillator (NRRAO) partition functions, 90 the development and benchmarking of a stateof-the-art computational approach that aims to reproduce total atomisation energies of small molecules within 10-15 cm À1 , 91 as well as the study of the reversible reaction C 2 H 3 + H 2 $ C 2 H 4 + H $ C 2 H 5 . 92 Since then, the underlying ATcT TN has been successively expanded to fulfil the needs of subsequent studies, such as those involving enthalpies of formation of key bromo-and iodomethanes, ethenes and ethynes, 93 the ring-opening dynamics of cyclopropyl and cyclopropylium (ATcT TN versions 1.128 and 1.130), 94 the bond dissociation energy and the adiabatic ionisation energy of CH (ATcT TN ver. 1.140), 62 the role of methanediol in the atmosphere (ATcT ver.…”