Metallic atomic hydrogen

Reduction reactions of metal oxides by hydrogen start with the dissociative adsorption of H2, which is a much more difficult process on oxides than on metals. Atomic hydrogen takes care of the actual reduction. Depending on how fast or how slow the dissociative adsorption is in comparison to the subsequent reduction reactions which comprise diffusion of atomic hydrogen into the lattice, reaction with oxygen and removal of the hydroxyl species formed, two limiting cases are distinguished [1,7]. 

The simplest form of spin-orbitals for a system with translational invariance are plane waves (PW) 9k r,a) = exp[ fe r]. This form was used in the first QMC study of metallic hydrogen [33]. It is particularly appealing for its simplicity and still qualitatively correct since electron-electron and electron-proton correlations are considered through the pseudopotential . The plane waves orbitals are expected to reasonably describe the nodal structure for metallic atomic hydrogen, but no information about the presence of protons appears in the nodes with PW orbitals. 

The unknown functions, Cij r),riij r) in (57) and (58) need to be parameterized in some way. In a first attempt we have chosen gaussians with variance and amplitude as new variational parameters [16]. This form was shown to be suitable for homogeneous electron gas [13]. Approximate analytical forms for ij r) and r]ij r), as well as for the two-body pseudopotential, have been obtained later in the framework of the Bohm-Pines collective coordinates approach [14]. This form is particularly suitable for the CEIMC because there are no parameters to be optimized. This trial function is faster than the pair product trial function with the LDA orbitals, has no problems when protons move around and its nodal structure has the same quality as the corresponding one for the LDA Slater determinant [14]. We have extensively used this form of the trial wave function for CEIMC calculations of metallic atomic hydrogen. 

Insulating molecular hydrogen Metallic molecular hydrogen Metallic atomic hydrogen Rock core... 

Huiberts, J.N. (1995) On the road to dirty metallic atomic hydrogen. Ph. D. thesis, Vrije Universiteit Amsterdam. 

If one or both cobalt atoms were replaced by other metal atoms, hydrogen peroxide was formed either as the main product or as an intermediate. Chang et al. [40] fotmd that dicobalt diporphyrins anchored on dibenzofuran (DBD) and xanthene (DPX), Fig. 7.8A, exhibited remarkable conformational flexibility, and in both cases, the complexes were able to reduce oxygen directly to water despite having large differences ( 4 A) in the interplanar separation of their metal centers. Two other anchoring systems, anthracene and bisphenylene, have also been successfully used to... 

Hydrogen atoms chemisorbed on a metal surface may be bonded to just one metal atom or may be bonded to two atoms in a symmetrical bridge. In each case, there are three normal modes. Sketch what these are, and indicate any degeneracies (assume the metal atoms to be infinitely heavy). 

The simplest case arises when the electronic motion can be considered in temis of just one electron for example, in hydrogen or alkali metal atoms. That electron will have various values of orbital angular momentum described by a quantum number /. It also has a spin angular momentum described by a spin quantum number s of d, and a total angular momentum which is the vector sum of orbital and spin parts with... 

Casassa S and Pisani C 1995 Atomic-hydrogen interaction with metallic lithium an ab /M/o embedded-cluster study Phys. Rev. B 51 7805... 

A process resulting in a decrease in touglmess or ductility of a metal due to absorjDtion of hydrogen. This atomic hydrogen can result, for instance, in the cathodic corrosion reaction or from cathodic protection. 

Step 1 Hydrogen molecules react with metal atoms at the catalyst surface The relatively strong hydrogen-hydrogen c bond IS broken and replaced by two weak metal-hydrogen bonds... 

For hydrogen and the alkali metal atoms in their ground configurations, or excited configurations involving promotion of the valence electron, there is only one electron with an unpaired spin. For this electron = - - or — and the corresponding electron spin part... 

Metal Acetylides. The replacement of a hydrogen atom on acetylene by a metal atom under basic conditions results in the formation of metal acetyhdes which react with water in a highly exothermic manner to yield acetylene and the corresponding metal hydroxide. Certain metal acetyUdes can be... 

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