Bonding in radon hexafluoride: An unusual relativistic problem?

Abstract

Radon hexafluoride is a bound species (bond length Rn–F: 2.008 Å) as demonstrated by correlation corrected relativistic ab initio calculations using IORAmm (infinite order regular approximation with modified metric) at the MP2 level of theory with a (24s20p13d8f)[15s13p8d4f]/aug-cc-pVDZ basis set. The calculated atomization energy is 226.9 kcal mol⁻¹ and the dissociation energy leading to Rn and 3F₂ is 126.6 kcal mol⁻¹. Results are in line with simple orbital-based predictions of possible relativistic effects. The relativistic effect for the atomization energy is −10.8 kcal mol⁻¹ rather than +27.7 kcal mol⁻¹ as predicted on the basis of Dirac–Hartree–Fock (DHF) calculations. The latter were flawed by the lack of correlation corrections and an erroneous polynomial fit of the potential energy surface in the vicinity of the global minimum.