5d Orbitals of xenon in atomic valence states and in the molecules XeF2 and XeCl2

Abstract

Energies for excited configurations and valence states of xenon are optimised by varying 5s, 5p, and 5d atomic orbital exponents. These calculations show that 5d orbitals are diffuse in d1 configurations, but are contracted with further promotion to the d levels. It is confirmed that promotion energies to 5d states may be large. For valence states derived with trigonal bipyramidal, octahedral, and pentagonal bipyramidal hybridisations, the most favourable estimates are respectively 9, 35, and 46 eV above the ground state.Additionally, some model calculations have been made for XeF2 and XeCl2 by use of the extended valence bond method of Hurley, Lennard-Jones, and Pople. The calculations for XeF2 suggest that the covalent bond structure F–Xe–F, involving 5dσ interactions, is energetically more favourable than structures depending on ionic contributions, such as F–Xe+F– and F–Xe2+F–. This confirms that the stabilisation of 5dσ orbitals by molecular environments can be sufficiently large that the 5d atomic promotion energies are recovered during bond formation. Xenon 5d orbitals are stabilised in XeCl2, but to a less extent than in XeF2. It is expected that 5d and 6s orbital bonding is important for XeF4 and XeF6.