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

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.

Automated summary

The thermochemistry of halocarbon species containing iodine and bromine is examined through an extensive interplay between new FPD style composite methods and a detailed analysis of all available experimental and theoretical determinations using the thermochemical network that underlies the ATcT. The study found that the convergence of composite thermochemistry methods is slower for halocarbon species containing iodine and bromine, leading to higher computational expense. Spin-orbit coupling was identified as a critical component, especially for iodine containing molecular species. This study provides accurate and reliable heats of formation for 38 halogen containing systems.