Muon transfer from the excited mesic hydrogen in the metastable 2s-state to helium nuclei

The rate of the molecular charge exchange of the excited muonic hydrogen in the 2s-state on helium nuclei is calculated. Resonance muon transfer is shown to occur with the formation of the intermediate excited complex ([(H μ)*He²⁺]2e)*. The resulting rates prove that the muon transfer from the 2s-state alone can not account for the experimental data on the muon transfer frompμ-atoms to⁴He nuclei.     

Potential energy surfaces for the interaction of atomic and diatomic hydrogen with lithium metal clusters

In this paper a modified CNDO/2 method is used to study the interaction of hydrogen atoms and molecules with molecular clusters simulating the (100) surface of solid lithium metal. The modification, described in an earlier papers, involves rescaling bicentric CNDO/2 energy contributions with known diatomic bond energies. Potential energy curves are calculated for six attack points by the hydrogen atom on the surface, and for one attack point by the molecule. The results indicate that in both atom and molecule forms hydrogen penetrates the surface and that the molecule most likely dissociates.     

Surface crossing in interaction of atomic hydrogen with a lithium metal cluster

Interaction of atomic hydrogen with a (4,1,4) lithium cluster, simulating the (100) metal surface, is studied using the diatomics-in-molecules method. Ground-and excited-state potential curves for normal approach ofH to some attack positions on the surface intersect or pseudo-intersect. The results reveal possible non-adiabatic character of the absorption process.     

Variation of atomic charges during proton transfer in hydrogen bonds

The point atomic charges in a number of ionic H-bonded systems are studied by ab initio calculations as functions of the proton transfer coordinate. In the proton-bound complexes of water–water, ammonia–ammonia, formamide–water, formamide–ammonia, and dimethylether–ammonia, the net atomic charges were obtained using Mulliken population analysis and from the diagonal elements of the atomic polar tensors calculated at the HF/4–31G and MP2/6–31 + G** levels. The dependence of the atomic charges upon the coordinate of the transferring proton was found to be close (within an error of 0.02 e) to a linear function for intermolecular distances in the 2.5–2.8 Å range. The obtained charge and charge flux dependencies highlight the electron redistribution during the proton transfer process and provide insights into the source of the high infrared (IR) intensities of stretching modes of N? H and O? H bonds undergoing hydrogen bonding. © 1994 by John Wiley & Sons, Inc.     

Combined SSF MO LCAO and correlation density functional method applied to adsorption of atomic hydrogen on lithium clusters

An SSF MO LCAO + CDF Method is developed, in which supplementary to a nonempirical SSF MO LCAO calculation the correlation energy of a many electron system is estimated as a functional of the electron density E_C[]. To check the effectiveness of this procedure for calculating the E_C[] functional, E_C is calculated for monohydrides of elements in the second and third columns of the periodic table. The SSF MO LCAO + CDF is applied to a comparative calculation of the adsorption of atomic hydrogen on lithium clusters with different multiplicity and the role of the electron correlation in this process is established.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 385–392, July–August, 1989.     

Model study of the nonadiabatic effects in the interaction of atomic hydrogen with lithium metal clusters

Study is made of the effects of adsorption site position on mutual arrangement and nonadiabatic coupling between the lowest two singlet potential energy surfaces of the Li₉(4, 1, 4)-H chemisorption system. Special attention is paid to a normal approach of H atom to Li₉ cluster. The necessary energy and coupling data are obtained by use of the method of the diatomics-in-molecules. The changes with the alteration of the adsorption site position of the degree of nonadiabatic behaviour of system is shown to be quite significant.     

Mathematical simulation of atomic hydrogen diffusion transfer through a bimetallic membrane

Mathematical simulation of atomic hydrogen diffusion transfer through a bimetallic membrane is performed under the approximation of an ideal lattice gas. Analytical expressions are derived for diffusion fluxes at different membrane orientations. The intensity of diffusion transfer of hydrogen atoms through a bimetallic membrane depends on the direction of transfer, provided that they have different solubilities in metal layers. It is shown that the effect of diffusion asymmetry must be taken into account when developing and using bimetallic membranes.     

Desorption of InOH from indium oxides under exposure to atomic hydrogen

Species desorbing from indium oxides under exposure to atomic hydrogen (H) were observed with a quadrupole mass spectrometer. The desorption of InOH was detected at a temperature as low as 410°C, which is in contrast with the fact that, with molecular hydrogen, a much higher temperature (850°C) was required to generate InOH. Upon the interruption of H generation, the InOH signal disappeared immediately, suggesting that H is involved in the reactions leading to InOH desorption. Relevance to the low-temperature cleaning of an InP surface with H is discussed.     

Reactions of atomic nitrogen and atomic hydrogen with methylacetylene

The reaction of nitrogen atoms with methylacetylene has been studied using a fast-flow low-pressure reactor coupled to a mass spctrometer by a nozzle-beam sampling system. Hydrogen atom concentrations were measured by ESR analysis. Experimental second-order rate constants for the consumption of N atoms, of C₃H₄, and for the formation of N₂ were determined in the temperature range of 283° to 485°K. Product profiles of all stable species and of hydrogen atoms and methyl radicals were obtained for different initial concentrations of the reactants. Two different reaction pathways can be distinguished: one provides for recombination of N atoms, and the second leads to the formation of cyano compounds and other hydrocarbons. Only the latter process is influenced by the addition of hydrogen atoms. Mechanisms for the two pathways are discussed.     

Semi-classical approach to intensity spectrum of atomic hydrogen

The intensity of the dipole spectrum of atomic hydrogen is re-examined with the aid of classical, semi-classical and quantum-mechanical approximations. Quantum-mechanical data can be approached semi-classically on condition the differences between the discrete time periods of hydrogen levels are applied in the calculations.     

Reactions involving hydrogen transfer from triosmium clusters to an activated nitrile

The reactions of H₂Os₃(CO)₁₀, Ia and H₂Os₃(CO)₉PMe₂Ph, Ib with CF₃CN have been investigated. Both la and Ib react with CF₃CN to give the products HOs₃[μ-η₂-(CF₃)CNH](CO)₉Land HOs₃[μ-η¹-NC(H)CF3](CO)₉L, IIa, IIIa, L = CO; IIb and IIIb, L = PMe₂Ph. IIb and IIIb have been characterized crystallographically. In each, one nitrile molecule was added to the cluster and one hydride ligand was transferred to the nitrile ligand, but in IIb the hydride was transferred to the nitrogen atom to form a CF₃CNH ligand which bridges an edge of the cluster while in IIIb the hydride was transferred to the carbon atom to form a CF₃(H)CN ligand which also bridges an edge of the cluster. On the basis of spectroscopic measurements IIa and IIIa are believed to have analogous structures. An isotope scrambling experiment established that the formation of Ilia occurs by an intramolecular process. IIa was decarbonylated to yield the compound HOs₃[μ₃-η₂-(CF₃)CNH](CO)₉, which is believed to contain a triply-bridging iminyl ligand. Ilia reacts with PMe₂Ph to give two mono-substitution products, one of which is IIIb.     

Mechanism of the hydrogen transfer from the OH group to oxygen-centered radicals: proton-coupled electron-transfer versus radical hydrogen abstraction

High-level ab initio electronic structure calculations have been carried out with respect to the intermolecular hydrogen-transfer reaction HCOOH+.OH-->HCOO.+H(2)O and the intramolecular hydrogen-transfer reaction .OOCH2OH-->HOOCH(2)O.. In both cases we found that the hydrogen atom transfer can take place via two different transition structures. The lowest energy transition structure involves a proton transfer coupled to an electron transfer from the ROH species to the radical, whereas the higher energy transition structure corresponds to the conventional radical hydrogen atom abstraction. An analysis of the atomic spin population, computed within the framework of the topological theory of atoms in molecules, suggests that the triplet repulsion between the unpaired electrons located on the oxygen atoms that undergo hydrogen exchange must be much higher in the transition structure for the radical hydrogen abstraction than that for the proton-coupled electron-transfer mechanism. It is suggested that, in the gas phase, hydrogen atom transfer from the OH group to oxygen-centered radicals occurs by the proton-coupled electron-transfer mechanism when this pathway is accessible.     

Enthalpy and entropy of transfer of hydrogen ion from water to mixed solvents

Attempts have been made to determine the enthalpy and entropy of transfer of H⁺ ion from water to mixed solvents using the calorimetric data of earlier experiments. The results are in qualitative agreement with the facts that ΔH _t ⁰ (H⁺) passes through an exothermic maximum andTΔS _t ⁰ passes through a minimum at about 20 to 30 wt% of organic solvent indicating the initial structure formation and the ultimate breakdown of the solvent structure with the addition of organic solvent.     

Theoretical rates for the emission of atomic hydrogen from a naphthalene cation

The statistical phase space theory (PST) in its orbital transition state version has been used to calculate the dissociation rate associated with the loss of atomic hydrogen from a polycyclic aromatic hydrocarbon molecule. The PST model has been applied to the naphthalene cation with input data obtained exclusively from first-principle calculations using density functional theory. Without any fitting parameters, the calculated dissociation rates are found to agree well with available measurements. The effects of vibrational anharmonicities are investigated and are shown to lower the dissociation rates by a factor of about five.     

A big step forward to graphene-based atomic hydrogen storage

Considered as the ultimate solution for the energy and environment crises,hydrogen energy plays a crucial role in the realization of worldwide carbon neutrality.There are three key issues for the practical utilization of hydrogen energy:high-capacity storage,safe transportation and reversible release,among which hydrogen storage is the first step.     

Ab initio study of oxygen atom transfer from hydrogen peroxide to trimethylamine

Unlike what has been theoretically proposed for ammonia oxidation with hydrogen peroxide, trimethylamine oxidation occurs with a concerted mechanism, which is favored even when an explicit water molecule is added or continuum solvent (water) is simulated.     

Ligand effects on hydrogen atom transfer from hydrocarbons to three-coordinate iron imides

A new β-diketiminate ligand with 2,4,6-tri(phenyl)phenyl N-substituents provides protective bulk around the metal without exposing any weak C-H bonds. This ligand improves the stability of reactive iron(III) imido complexes with Fe═NAd and Fe═NMes functional groups (Ad = 1-adamantyl; Mes = mesityl). The new ligand gives iron(III) imido complexes that are significantly more reactive toward 1,4-cyclohexadiene than the previously reported 2,6-diisopropylphenyl diketiminate variants. Analysis of X-ray crystal structures implicates Fe═N-C bending, a longer Fe═N bond, and greater access to the metal as potential reasons for the increase in C-H bond activation rates.     

Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins

Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure–reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an Ir^II–H bond dissociation free energy around 44 kcal mol⁻¹, which is formed after reductive ³MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer.

Upon irradiation with visible light, an iridium hydride complex undergoes hydrogen atom transfer (HAT) to unactivated olefins in presence of a sacrificial electron donor and a proton source.