Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

An accurate coupled-cluster (CC) based model chemistry was applied to calculate reliable thermochemical quantities for hydrofluorocarbon derivatives including radicals 1-fluoroethyl (CH3-CHF), 1,1-difluoroethyl (CH3-CF2), 2-fluoroethyl (CH2F-CH2), 1,2-difluoroethyl (CH2F-CHF), 2,2-difluoroethyl (CHF2-CH2,), 2,2,2-trifluoroethyl (CF3-CH2), 1,2,2,2-tetrafluoroethyl (CF3-CHF), and pentafluoroethyl (CF3-CF2). The model chemistry used contains iterative triple and perturbative quadruple excitations in CC theory, as well as scalar relativistic and diagonal Born-Oppenheimer corrections. To obtain heat of formation values with better than chemical accuracy perturbative quadruple excitations and scalar relativistic corrections were inevitable. Their contributions to the heats of formation steadily increase with the number of fluorine atoms in the radical reaching 10 kJ/mol for CF3-CF2. When discrepancies were found between the experimental and our values it was always possible to resolve the issue by recalculating the experimental result with currently recommended auxiliary data. For each radical studied here this study delivers the best heat of formation as well as entropy data

Theoretical and Thermochemical Network Approaches To Determine the Heats of Formation for HO2 and Its Ionic Counterparts

The purpose of this study is to give reliable and accurate thermochemical data for HO2, HO2+, and HO2. Their heats of formation were determined using quantum chemical calculations with the aid of high-accuracy coupled-cluster methods taking account of zero-point vibrational energies, scalar-relativistic effects, and the deficiencies of the Born-Oppenheimer approximation. Furthermore, a thermochemical network, containing 14 experimental and 7 theoretical reaction enthalpies, was set up to determine even more accurate heats of formation. The iteratively reweighted least-squares solution of the network yielded the best heat of formation estimates, which are Delta H-f(0)degrees(HO2) = 14.85 +/- 0.22, Delta H-f(298)degrees(HO2) = 11.92 +/- 0.22, Delta H-f(0)degrees(HO2+) = 1110.56 +/- 0.40, Delta H-f(298)degrees(HO2+) = 1107.64 +/- 0.40, Delta H-f(0)degrees(HO2) = -89.04 +/- 0. 39, and Delta H-f(298)degrees(HO2) = -91.75 +/- 0.39 kJ/mol. In addition, in line with previous accurate data Delta H-f(0)degrees(OH) = 37.25 +/- 0.03, Delta H-f(0)degrees(OH+) = 1293.20 +/- 0.03, and Delta H-f(0)degrees(H2O2) = -129.48 +/- 0.06 kJ/mol were also delivered by our network

High Accuracy Quantum Chemical and Thermochemical Network Data for the Heats of Formation of Fluorinated and Chlorinated Methanes and Ethanes

Reliable heats of formation are reported for numerous fluorinated and chlorinated methane and ethane derivatives by means of an accurate thermochemical protocol, which involves explicitly correlated coupled-cluster calculations augmented with anharmonic, scalar relativistic, and diagonal Born–Oppenheimer corrections. The theoretical results, along with additional experimental data, are further enhanced with the help of the thermochemical network approach. For 28 species, out of 50, this study presents the best estimates, and discrepancies with previous reports are also highlighted. Furthermore, the effects of the less accurate theoretical data on the results yielded by thermochemical networks are discussed

Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

An accurate coupled-cluster (CC) based model chemistry was applied to calculate reliable thermochemical quantities for hydrofluorocarbon derivatives including radicals 1-fluoroethyl (CH₃–CHF), 1,1-difluoroethyl (CH₃–CF₂), 2-fluoroethyl (CH₂F–CH₂), 1,2-difluoroethyl (CH₂F–CHF), 2,2-difluoroethyl (CHF₂–CH₂), 2,2,2-trifluoroethyl (CF₃–CH₂), 1,2,2,2-tetrafluoroethyl (CF₃–CHF), and pentafluoroethyl (CF₃–CF₂). The model chemistry used contains iterative triple and perturbative quadruple excitations in CC theory, as well as scalar relativistic and diagonal Born–Oppenheimer corrections. To obtain heat of formation values with better than chemical accuracy perturbative quadruple excitations and scalar relativistic corrections were inevitable. Their contributions to the heats of formation steadily increase with the number of fluorine atoms in the radical reaching 10 kJ/mol for CF₃–CF₂. When discrepancies were found between the experimental and our values it was always possible to resolve the issue by recalculating the experimental result with currently recommended auxiliary data. For each radical studied here this study delivers the best heat of formation as well as entropy data