François Gilardoni

Excited state properties of Cr3+ in Cs2NaYCl6 and Cs2NaYBr6: A density functional study

The ground and excited state properties of the Cr3+ ion doped into the cubic host lattices Cs2NaYCl6 and Cs2NaYBr6 have been studied using density functional theory. A new symmetry based technique was employed to calculate the energies of the multiplets 4A2g, 4T2g, 2Eg, and 4T1g. The geometry of the CrX3−6 cluster was optimized in the ground and excited states. A Madelung correction was introduced to take account of the electrostatic effects of the lattice. The experimental Cr–X distance in the ground state can be reproduced to within 0.01 A for both chloride and bromide systems. The calculated d–d excitation energies are typically 2000–3000 cm−1 too low. An energy lowering is obtained in the first 4T2g excited state when the octahedral symmetry of CrX3−6 is relaxed along the eg Jahn–Teller coordinate. The geometry corresponding to the energy minimum is in excellent agreement with the 4T2g geometry derived from high‐resolution optical spectroscopy of Cs2NaYCl6:Cr3+. It corresponds to an axially compressed...

Density functional investigation of the mechanism of the selective catalytic reduction of NO by NH3 over vanadium oxide model clusters

Quantum chemical calculations using the density functional theory were performed to model the mechanism of selective catalytic reduction of NO by NH{sub 3} on a supported vanadium oxide monolayer. In the first step, the adsorption of NH{sub 3} on a bimetallic cluster representative of vanadium oxide, containing a terminal V=O adjacent to a V-OH group, was investigated. The calculations indicate that NH{sub 3} may be strongly adsorbed on V-OH (Broensted acid site) as NH{sub 4(ads)}{sup +}; subsequently, NO reacts with this activated NH{sub 3} to yield the reaction products N{sub 2} and H{sub 2}O. The present results give support to a dual-site Eley-Rideal-type mechanism involving a Broensted site. 38 refs., 5 figs., 2 tabs.

Theoretical study of interstellar hydroxylamine chemistry: protonation and proton transfer mediated by H3+

Protonated species are known to play a key role for ion-molecule reactions in gas phase interstellar chemistry. As hydroxylamine (H2NOH) has never been observed as an interstellar molecule, a detailed theoretical investigation of the protonation of H2NOH is carried out at high level of quantum chemical theories (CCSD(T) and DFT-B3LYP). As protonation may occur directly by reaction with H+ or mediated by H3+, both processes are investigated on the nitrogen and the oxygen sites of hydroxylamine. The present results show that the N-protonated form is more stable than the O-protonated one and that the protonation initiated by H3+ is by far less exothermic than the other one. A particular attention is paid to the intramolecular rearrangement leading from H3NOH+ to H2NOH2+ which involves a highly energetic transition state exhibiting proton bridged between N and O sites. As this barrier is too high to be easily overcome in the interstellar medium, an alternative process mediated by H2 and involving a bridged H3+ as a transition state is considered. The calculations show that the corresponding activation energy is significantly lowered.

Theoretical investigation of the adsorption of methanol on the (110) surface of γ-alumina

The adsorption of methanol on the (110) surface of γ-alumina was investigated using both ab initio and density functional theory quantum chemical methods. A [Al3O9H10]+ cluster model comprising one tetrahedral and two octahedral aluminum cations were used to describe the surface and the mechanism of adsorption of methanol. This has allowed us to rationalize the stable structures of adsorbate and the mode of bonding. The IR frequency shifts between the gas phase and the adsorbed species were also calculated and they exhibit good agreement with experiment.

A comparison of ground- and excited-state properties of gas phase and crystalline ruthenocene using density functional theory

The ground- and excited-state properties of both gas phase and crystalline ruthenocene, Ru(cp)2, are investigated using density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet splittings of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between a given Ru(cp)2 molecule and its first shell of neighbors. The overall agreement between experimental and calculated ground- and excited-state properties is very good as far as absolute transition energies, the Stokes shift and the geometry of the excited states are concerned. An additional energy lowering in the 3B2 component of the 5a1′→4e1″ excited state is obtained when the pseudolinear geometry of Ru(cp)2 is relaxed along the low-frequency bending vibration.

A comparison of ground- and excited-state properties of [Ru(bz)2]2+ and bis(?6-benzene)ruthenium(II)p-toluenesulfonate using the density functional theory

The ground‐ and excited‐state properties of both [Ru(bz)2]2+ and crystalline bis(η6‐benzene)ruthenium(II) p‐toluenesulfonate are investigated using the density functional theory. A symmetry‐based technique is employed to calculate the energies of the multiplet structure splitting of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between the [Ru(bz)2]2+ system and its first shell of neighbor molecules. The overall agreement between experimental and calculated ground‐ and excited‐state properties is good, as far as the absolute transition energies, the Stokes shift, and the geometry of the excited states are concerned. The calculated d‐d excitation energies of the isolated cluster are typically 1000–2000 cm−1 too low. An energy lowering is obtained in a1g→e1g(3E1g) excited state when the geometry of [Ru(bz)2]2+ is bent along the e1u Renner–Teller active coordinate. It vanishes as the crystal packing is taken into account. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1343–1353, 1999

Density-functional investigation of the excited state properties and the Jahn-Teller effect in [CrX6]3- (X=Cl,Br)

SummaryThe luminescence of [CrX6]3− X=Br−, Cl− has been studied through density functional theory (DFT) using both deMon and ADF codes. Multiplet energies4A2,2E,4T2, and4T1 have been expressed as energies of non-redundant single determinants and calculated as in Ref. [1]. The influence of the metal ligand distance on the multiplet energies has been investigated. Of particular interest to this work is the Jahn-Teller effect distortion. We found that the system moves to a more stable geometry when the axial bond length is compressed and the equatorial one elongated in agreement with the experimental value.

Applications of density functional theory to identify reaction pathways for processes occurring in zeolites and on dispersed metal oxides

The use of quantum chemical calculations to represent elementary processes involved in catalyzed reactions is illustrated through several examples. Density functional theory is applied to obtain information about the dynamics of proton mobility in H-ZSM-5, the activation barriers for H 2 O 2 synthesis over Pd-ZSM-5, and the initial steps in the oxidative dehydrogenation of C 3 H 8 over V 2 O 5 .