Reliable Potential Energy Surfaces for the Reactions of H2O with ThO2, PaO2(+), UO2(2+), and UO2(.) (original) (raw)
Related papers
Toward an Understanding of the Hydrogenation Reaction of MO2 Gas-Phase Clusters (M = Ti, Zr, and Hf)
The Journal of Physical Chemistry A, 2013
A theoretical investigation using density functional theory (DFT) has been carried out in order to understand the molecular mechanism of dihydrogen activation by means of transition metal dioxides MO 2 (M = Ti, Zr and Hf), according to the following reaction: MO 2 + H 2 → MO + H 2 O. B3LYP/6-311++G(2df,2pd)/SDD methodology was employed considering two possible reaction pathways. As first step the hydrogen activation by M=O bonds yields to metal-oxo hydride intermediates O=MH(OH). This process is spontaneous for all metal dioxides, and the stability of the O=MH(OH) species depends on the transition metal center. Subsequently, the reaction mechanism splits into two paths; the first one takes place passing through the M(OH) 2 intermediates yielding to products whereas the second one corresponds to the direct formation of the product complex OM(H 2 O). A two state reactivity mechanism was found for TiO 2 system whereas for ZrO 2 and HfO 2 no spin-crossing processes were observed. This is confirmed by CASSCF/CASPT2 calculations for ZrO 2 that lead to the correct ordering of electronic states not found by DFT. The results obtained in the present paper for MO 2 molecules are consistent with the observed reactivity on surfaces.
Theoretical Investigation of the H 3 O + (H 2 O) 4 Cluster
The Journal of Physical Chemistry A, 2001
The low-lying minima on the Born-Oppenheimer potential energy surface of the H 3 O + (H 2 O) 4 cluster are investigated by effective valence bond (EVB), density functional, and MP2 methods. Although Becke3LYP and MP2 calculations predict the same global minimum structure, the relative energies of various structures obtained by these two approaches differ by up to 1.7 kcal/mol. Even larger differences are found between the relative energies calculated at the EVB and MP2 levels of theory. Vibrational spectra are calculated for each of the minimum energy species.
Journal of Molecular Structure-theochem, 2006
Theoretical investigations on the kinetics of the elementary reaction H2O2+H→H2O+OH were performed using the transition state theory (TST). Ab initio (MP2//CASSCF) and density functional theory (B3LYP) methods were used with large basis set to predict the kinetic parameters; the classical barrier height and the pre-exponential factor. The ZPE and BSSE corrected value of the classical barrier height was predicted to be 4.1 kcal mol−1 for MP2//CASSCF and 4.3 kcal mol−1 for B3LYP calculations. The experimental value fitted from Arrhenius expressions ranges from 3.6 to 3.9 kcal mol−1. Thermal rate constants of the title reaction, based on the ab initio and DFT calculations, was evaluated for temperature ranging from 200 to 2500 K assuming a direct reaction mechanism. The modeled ab initio-TST and DFT–TST rate constants calculated without tunneling were found to be in reasonable agreement with the observed ones indicating that the contribution of the tunneling effect to the reaction was predicted to be unimportant at ambient temperature.
The Potential Energy Surface of the H~ 2O~ 2 System
AIP Conference Proceedings, 2006
The potential energy surfaces (PES) for the singlet and triplet H 2 O 2 molecular system were studied by using the CASSCF, CASPT2, QCISD, QCISD(T), and CCSD(T) methods with the aug-cc-pVDZ, aug-cc-pVTZ, and 6-311+G(3df,2p) basis sets. The CASSCF and CASPT2 results show some significant differences from the QCISD, QCISD(T), and CCSD(T) calculations. The QCISD(T)//QCISD and CCSD(T)//QCISD calculations were found to be suitable for examining most of the species and reaction paths on the H 2 O 2 PES except for a few open shell species which have a multi-reference character. The CASSCF and CASPT2 methods were found to be better suited for treating these open shell species. Consistent with previous theoretical and experimental work we find the hydrogen abstraction reaction 1 O + H 2 O 2 OH + 2 OH to have a small or no energy barrier suggesting this pathway may have relevance to the astrochemical formation of hydrogen peroxide in an extraterrestrial environment.
Theoretical studies of O2?:(H2O)n clusters
Journal of Computational Chemistry, 1986
The interaction of superoxide ion O2 with up to four water molecules [0;. ; (H2O).. , n = 1,2,4] has been investigated using ab initio molecular orbital theory. The binding energy of O2; H2O is calculated to be -20.6 kcal/mol in good agreement with gas phase experimental data. At the MP3/6-31G. level the O2; H2O complex has a C20. structure with a double (cyclic) hydrogen bond between 0;. and H2O. A C. structure with a single hydrogen bond is only 0.7 kcal/molless stable. Interaction of H2O with the doubly occupied 1f* orbital of O2 is preferred slightly over interaction with the singly occupied 1f. orbital. Natural bond orbital analysis suggests that both electrostatic and charge transfer interactions are important in anionic complexes. The charge transfer occurs pt'edominantly in the O2 -H2O direction and is important in determining the relative stabilities of the different structures and states. Singly and doubly hydrogen-bonded structures for the O2 ;(H2O)2 and 0;. :(H2O). clusters were found to be similar in stability and the increase in binding of the cluster becomes smaller as each additional water molecule is added to the cluster.
Energetic and topological analysis of the reaction of Mo and Mo2 with NH3, C2H2, and C2H4 molecules
Journal of Computational Chemistry, 2004
The Density functional theory has been applied to characterize the structural features of Mo 1,2 -NH 3 ,-C 2 H 4 , and -C 2 H 2 compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo 1,2 -NH 3 ), the interaction between Mo (or Mo 2 ) and C 2 H 4 (or C 2 H 2 ) are the low-spin (Mo-C 2 H 4 and -C 2 H 2 ) and high-spin (Mo 2 -C 2 H 4 and -C 2 H 2 ) complexes. In the ground state of Mo 1,2 -C 2 H 4 and -C 2 H 2 , the metal-center always reacts with the COC center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a -acceptor ligand correlates with a maximum charge transfer from the metal center to the COC bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the COC basin. The interaction between Mo 1,2 and C 2 H 4 (or C 2 H 2 ) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo 1,2 and NH 3 , and the partners are bound by an electrostatic interaction.
The Journal of Chemical Physics, 2010
Localized molecular orbital energy decomposition analysis and symmetry-adapted perturbation theory ͑SAPT͒ calculations are used to analyze the two-and three-body interaction energies of four low-energy isomers of ͑H 2 O͒ 6 in order to gain insight into the performance of several popular density functionals for describing the electrostatic, exchange-repulsion, induction, and short-range dispersion interactions between water molecules. The energy decomposition analyses indicate that all density functionals considered significantly overestimate the contributions of charge transfer to the interaction energies. Moreover, in contrast to some studies that state that density functional theory ͑DFT͒ does not include dispersion interactions, we adopt a broader definition and conclude that for ͑H 2 O͒ 6 the short-range dispersion interactions recovered in the DFT calculations account about 75% or more of the net ͑short-range plus long-range͒ dispersion energies obtained from the SAPT calculations.
Physical Chemistry Chemical Physics, 2012
The OH + CO -H + CO 2 reaction is important in combustion, atmospheric, and interstellar chemistry. Whereas the direct reaction has been extensively studied both experimentally and theoretically, the reverse reaction has received relatively less attention. Here we carry out a quasiclassical trajectory study of the hyperthermal H + CO 2 -OH + CO reaction on a new interpolated potential energy surface based on the M06-2X density functional. The results reveal for the first time quantitative agreement with experiment for the reaction cross sections in the range of relative translational energies 1.2-2.5 eV. We attribute this excellent agreement to both the quality of the M06-2X energies, which closely reproduce CCSD(T) energies, and to the potential surface construction strategy that emphasizes both the direct and reverse reactions.