Hydrogen atom solid phases

Figure 1 Eneigy profiles for formation of a linear dimer of for-mamides. The CO of one monomer and the NH of the other are co-linear and they are oriented with the oxygen atom facing the hydrogen atom. Solid curve gas-phase profile light dashed curve solvation contribution from continuum model heavy dashed curve net profile in water...

Neutron diffraction studies have shown that in both systems Pd-H (17) and Ni-H (18) the hydrogen atoms during the process of hydride phase formation occupy octahedral positions inside the metal lattice. It is a process of ordering of the dissolved hydrogen in the a-solid solution leading to a hydride precipitation. In common with all other transition metal hydrides these also are of nonstoichiometric composition. As the respective atomic ratios of the components amount to approximately H/Me = 0.6, the hydrogen atoms thus occupy only some of the crystallographic positions available to them. 

The effects of transfer of atoms by tunneling may play an essential role in a number of phenomena involving the transfer of atoms and atomic groups in the condensed phase. One may expect that these effects may exist not only in the proton transfer reactions considered above but also in such processes as the diffusion of hydrogen atoms and other light ions (e.g., Li+) in liquids, tunnel inversion and isomerization in some molecules, quantum diffusion of defects and light atoms in the electrode at cathodic incorporation of the ions, ion transfer across the liquid/solid interface, and low-temperature chemical reactions. 

Proton transfer to negatively charged hydrogen atoms has attracted the attention of many chemists over the last two decades. This process plays an important role in many chemical and biochemical phenomena that occnr in the gas phase, in solution, and in the solid state [1-3], For example, direct proton attack on hydride ligands generates transition metal dihydrogen complexes which are then involved in various catalytic transformations [4] ... 

The hydrogen is, at small hydrogen to metal ratios (H M<0.1), exothermically dissolved (solid solution, a-phase) in the metal. The metal lattice expands proportionally to the hydrogen concentration by approximately 2-3 A per hydrogen atom [31]. At greater hydrogen concentrations in the host metal (H M > 0.1), a strong... 

It is helpful to choose conditions under which the ionic reactions will predominate In the solid phase at low temperature secondary processes of decomposition and freely diffusing radical interactions are expected to be greatly inhibited. The solid lattice will tend to prevent fragmentation and to promote rapid energy dissipation so that the formation of radicals with the possible exception of hydrogen atoms will be largely prevented. Furthermore, alkyl radical reactions are restricted to radical pairs that are formed adjacent to one another... 

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