OH Binding Energies Research Articles

Ab initio study of the hydrogen abstraction reaction H 2O 2+OH→HO 2+H 2O

Elementary hydrogen abstraction reaction between OH radical and H 2O 2 molecule to yield H 2O and HO 2 molecules has been investigated by ab initio molecular orbital calculations. In addition to the well known reactants and products structures we have located two stationary structures, an intermediate complex OH–H 2O 2 and a transition state H 3O 3 structures. The binding energy of OH–H 2O 2 and the reaction energy are predicted to be, respectively, −3.7 and −31.4 kcal mol −1. The activated complex is found to be more stable than the reactants by 0.9 kcal mol −1 and less stable than the intermediate complex by 2.8 kcal mol −1. These results are used to give a tentative explanation of the observed anomalous behavior of the measured rate constant k( T) as a function of temperature T and to try for an interpretation on the physical origin of the two terms in the, non-Arrhenius, fitted expression of k( T) proposed by Hipler et al. k(T)=[2.0×10 12 exp(−215 K/T)+1.7×10 18 exp(−14,800 K/T)] cm 3 mol −1 s −1 for 240≤T≤1600 K.

Ab initio calculation of proton barrier and binding energy of the (H 2O)OH − complex

The very low barrier (of the order of 1 kJ mol −1) to proton transfer in the (H 2O)OH − complex is accurately computed by the coupled-cluster method including single and double excitations plus perturbative corrections for triple excitations [CCSD(T)]. By virtue of the coupled-cluster R12 method [CCSD(T)-R12], which employs explicitly correlated wave functions, results are obtained close to the limit of a complete basis set of atomic orbitals (AOs). The basis-set superposition error is avoided by applying the full function counterpoise approach to the three fragments OH −, H +, and OH −. The most accurate computed value for the proton barrier amounts to δ=0.9±0.3 kJ mol −1, which is 4–5 times this value below the lowest vibrational energy level. The three lowest vibrational energy levels are calculated from a one-dimensional potential energy curve describing the position of the bonding proton between the two OH − fragments. The electronic binding energy with respect to dissociation into H 2O and OH − is estimated to D e =109±10 kJ mol −1 at the level of explicitly correlated CCSD(T)-R12 theory.

Electronic structure and magnetism in 4 -transition metal clusters

We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of Oh and Ih clusters as a function of the atomic number along the 4 d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.

Successive OH Binding Energies of M(OH)n+ for n = 1−3 and M = Sc, Ti, V, Co, Ni, and Cu

The M(OH)n+ geometries, for n = 1−3, have been optimized and the zero-point energies computed using the B3LYP approach. The calculations show that strong bonds are formed for the early metals, and much weaker bonds are formed for the late metal atoms. The successive OH bond energies have been computed at the CCSD(T) level for n = 1 and 2. The M+−OH bond energies are in good agreement with the guided ion beam results. This implies that the CID values for TiOH+, VOH+, and CoOH+, and the photodissociation value for CoOH+ are accurate, but that the CID values for ScOH+ and NiOH+ are too small. The B3LYP binding energies are found to be in qualitative agreement with the CCSD(T) results. The relative size of the first and second OH binding energies at the B3LYP level disagrees with the CCSD(T) for Sc+, Ti+, and V+. The B3LYP results show that the third OH binding energy for Ti+ and V+ will be large (85 kcal/mol, or more), while for the remaining systems the third OH is electrostatically bound, with a binding energy of only about 30 kcal/mol.

The successive OH binding energies of Sc(OH) n+ for n = 1−3

The geometries of Sc(OH) n +, for n = 1–3, have been optimized and the zero-point energies computed using the B3LYP approach. The successive OH bond energies have been computed at the CCSD(T) level for ScOH + and Sc(OH) 2 +. The computed result for ScOD + is in excellent agreement with the recent experiment of Armentrout and co-workers. There is a dramatic drop for the third OH binding energy, because Sc + has only two valence electrons and therefore the bonding changes when the third OH is added. The difference between the B3LYP and CCSD(T) OH binding energies for the first two OH groups is discussed.

ChemInform Abstract: Gas Phase Water and Hydroxyl Binding Energies for Monopositive First‐Row Transition‐Metal Ions.

AbstractM+‐OH2 and M+‐OH binding energies of first‐row transition metals are determined by means of collision‐induced dissociation in a triple‐quadrupole mass spectrometer.

The thermodynamics of water and hydrogen solubility in fused silica

A statistical thermodynamic model of the solubility of water vapor in glass is developed as an extension of previous models of monatomic and diatomic gas solubility in glass. The model predicts the p 1 2 dependence of water vapor solubility in fused silica and indicates the binding energies of dissociated H and OH species to be about −63 and −99 kcal/mol, respectively. The OH binding energy is found to be slightly temperature dependent, namely E OH(0) = −81.3−0.0163 T. The tendency of chemical solubility of H 2 to predominate over physical solubility above 500°C correlates with the model equations for H 2 solubility.