Noble Gas Compounds: Reliable Computational Methods

Abstract

Because of the general interest in the bonding in noble gas (Ng) compounds and the lack of experimental data coupled with large discrepancies, reliable theoretical calculations are very important for the prediction of their structures and thermodynamics. We describe an approach for the prediction of heats of formation to ±1 kcal mol −1 (chemical accuracy) based on molecular orbital theory level using coupled cluster (CCSD(T), coupled cluster with single and double excitations plus a perturbative triples correction) theory extrapolated to the complete basis set (CBS) limit with the correlation‐consistent basis sets including relativistic effective core potentials (RECPs). Additional corrections to the valence correlation energies include core–valence (CV) correlation, molecular scalar relativistic corrections, atomic spin–orbit corrections, and zero‐point vibrational energies. Applications of this approach for the determination of the structure of XeF 6 , the heats of formation of the xenon fluorides and krypton fluorides, and the methyl cation affinities (MCAs) of the Ngs are described. XeF 6 is predicted to have C 3 v symmetry only at the highest computational levels. The experimental heats of formation of XeF 4 and XeF 6 require significant revision. The predicted heats of formation for KrF 4 and KrF 6 show that it will be extremely difficult to synthesize these compounds. The calculations show that there are serious issues with the experimental MCAs of all of the Ngs except for Ne.