Non-local, density functional calculations have been performed on the ground and low-lying excited states of the 3d transition metal monoxide and monosulfide molecules. Periodic trends in properties such as bond lengths, bond energies, vibrational force constants and dipole moments are examined. The variations in the bond lengths and energies are compared to those in the monoxide and monosulfide solids. Analysis of the electronic structures of the molecules reveals the d-orbital splitting to be d π > d σ ≥ d δ and shows the non-bonding role of the d σ and d δ functions. This sequence mirrors that in the electronically related dichloride molecules and leads to similarities in the periodic trends with those in the solids. Systematic errors in the calculated bond energies and vibrational frequencies are identified. The successful use of a correctly parameterized ligand-field model is reported allowing quantitative reproduction of the 'd-d' spectra of the monoxide molecules and the prediction of band positions of unassigned transitions.
Computational detailsAll density functional calculations were performed here using the 'DeFT' code written by St-Amant 14 in the linear combination of Gaussian-type orbitals (LCGTO) framework. All the reported calculations used the Vosko-Wilk-Nusair 15 local spin density (LSD) approximation of the correlation part of the exchange-correlation potential with non-local corrections using the Becke 16 functional for exchange and the Perdew 17 func-Paper a906523g
The geometries and vibrational frequencies of the hydrogen and halogen peroxides XOOXЈ and the XOO and XO fragments (X, XЈ = H, F, Cl, Br or I) have been studied using non-local density functional theory. The X-O, XЈ-O and O-O bond energies have been calculated and likely dissociation paths for these atmospherically important or potentially important molecules suggested. The sulfur analogues have also been examined. A unified model for these chemically diverse species is presented based on the interaction between O 2 and X ؒ ؒ ؒ X fragments. The correlation between their electronic structures is outlined. The antibonding nature of the interaction between the halogen lone pairs and the π electrons of the O 2 fragments causes lengthening and weakening of the halogen-oxygen bonds. The electronegativity of X and XЈ determines the extent and direction of the electron transfer between the O 2 and X ؒ ؒ ؒ X fragments. The O-O bond order is thus sensitive to the nature of the substituents and the multiple bond character decreases steadily as the electronegativity of X and XЈ decreases. The O-O bond strengths, though, are also affected by steric interactions between the halogen 'lone pairs'. The O-O bonds in the HO-OXЈ species are thus much stronger than the bond orders and lengths suggest.
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