Solid atomic hydrogen

A new, low-pressure, plasma-assisted proeess for synthesising diamonds has been found by Roy et al [83,84]. An intimate mixture of various forms of carbon with one of many metals (e.g., Au, Ag, Fe, Cu, Ni) is exposed to a microwave plasma derived from pure hydrogen at temperatures ranging from 600-1000 °C. Roy et al postulate a mechanism in which a solid solution of atomic hydrogen and the metal. Me, facilitates dissolution of carbon to form molten droplets of Me -Cj,-H. Diamonds nucleate at the surface of the droplets as the temperature is reduced. 

Figure 1. The electron momentum density for atomic hydrogen measured by EMS for the indicated energies compared with the square of Schrodinger wave function (solid curve) [4].

Figure 5. Isotherms of hydrogen gas (pressure p atm) in equilibrium with absorbed hydrogen in LaNi5 (concentration H atoms/LaNi5). Notice the alpha-region is where hydrogen is in solid solution, the (alpha+beta)-region is made-up of both solid solution hydrogen and hydrides, and the beta-region is...

The atomic hydrogen in the chamber reacts with and removes hydrogen atoms from methyl radicals attached to the substrate surface in order to create molecular hydrogen, leaving a clear solid surface for further deposition of free radicals. 

Thallium(I) hydride has been identified spectroscopically in the products of an electric discharge in hydrogen at a thallium cathode, or from thallium and atomic hydrogen.343 An unstable polymeric solid has also been reported.344 The borohydride TIBH4 can be obtained by reacting Tl1 compounds with LiBHU, and T1A1H4 is formed similarly 344 the borohydride, which has an ionic lattice, can also be prepared from KBH4 and aqueous TlNOs-345... 

With carboxylic acids, the simple dimeric species are reasonably persistent in solution (and the gas phase), but the more extended structures are generally limited to the solid state. Hydrogen bonding between carbonyl oxygen atoms and amino N-H groups has... 

In molecular solids, atoms or molecules bond using hydrogen bonds or dipole-dipole dispersion forces. This bond occurs when temporary dipoles are induced in adjacent atoms. 

At ultrahigh pressure and low temperature, such as 250 GPa and 77 K, solid molecular hydrogen transforms to a metallic phase, in which the atoms are held together by the metallic bond, which arises from a band-overlap mechanism. Under such extreme conditions, the H2 molecules are converted into a linear chain of hydrogen atoms (or a three-dimensional network). This polymeric H structure with a partially filled band (conduction band) is expected to exhibit metallic behavior. Schematically, the band-overlap mechanism may be represented in the following manner ... 

In these experiments, there was no double-resonance tagging, so all of the HI moieties were available for photodissociation. What is observed experimentally is the resulting atomic hydrogen time-of-flight distribution which is obtained by using the HRTOF technique (Ashfold et al. 1992 Schneider et al. 1990 Wen et al. 1994). This method provides excellent resolution and S/N compared to other TOF methods. The dominant features (solid curves) are due to HI monomer. However, upon magnification, features are seen that are due to... 

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