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Frantsevich Institute for Problems of Materials Science, NAS of Ukraine
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Papers by David Urch
Mineralogical Magazine, 1989
X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in b... more X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in both valence band and core orbitals. As core vacancies are the initial states for X-ray emission, a knowledge of their energies for all atoms in a mineral enables all the X-ray spectra to be placed on a common energy scale. X-ray spectra are atom specific and are governed by the dipole selection rule. Thus the individual bonding roles of the different atoms are revealed by the fine structure of valence X-ray peaks (i.e. peaks which result from electron transitions between valence band orbitals and core vacancies). The juxtaposition of such spectra enables the composition of the molecular orbitals that make up the chemical bonds of a mineral to be determined.Examples of this approach to the direct determination of electronic structure are given for silica, forsterite, brucite, and pyrite. Multi-electron effects and developments involving anisotropic X-ray emission from single crystals are ...
Canadian Journal of Chemistry, 1960
The chemistry of hot hydrogen atoms has been studied using tritium of high kinetic energy as prod... more The chemistry of hot hydrogen atoms has been studied using tritium of high kinetic energy as produced by nuclear recoil. The possibilities and limitations of this technique are discussed using a collision theory for reactions of atoms having a very high initial energy. Using this theory and certain experimental data, it is concluded that hot hydrogen atoms react to combine with organic molecules at very high collision efficiency (of the order of approximately 0.2 to 0.4) in the energy range 3–10 ev. There is no indication that collisions at much higher energies lead to combination. With most systems, e.g. alkanes, a wide variety of reactions is observed. The systematics of these hot reactions is discussed and evidence on their detailed mechanism is presented. It appears that most products are formed by a fast displacement of an atom or group by the hot hydrogen. There is no evidence for the formation of a common, internally equilibrated, collision complex which decays on a statistic...
Mineralogical Magazine, 1989
X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in b... more X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in both valence band and core orbitals. As core vacancies are the initial states for X-ray emission, a knowledge of their energies for all atoms in a mineral enables all the X-ray spectra to be placed on a common energy scale. X-ray spectra are atom specific and are governed by the dipole selection rule. Thus the individual bonding roles of the different atoms are revealed by the fine structure of valence X-ray peaks (i.e. peaks which result from electron transitions between valence band orbitals and core vacancies). The juxtaposition of such spectra enables the composition of the molecular orbitals that make up the chemical bonds of a mineral to be determined.Examples of this approach to the direct determination of electronic structure are given for silica, forsterite, brucite, and pyrite. Multi-electron effects and developments involving anisotropic X-ray emission from single crystals are ...
Canadian Journal of Chemistry, 1960
The chemistry of hot hydrogen atoms has been studied using tritium of high kinetic energy as prod... more The chemistry of hot hydrogen atoms has been studied using tritium of high kinetic energy as produced by nuclear recoil. The possibilities and limitations of this technique are discussed using a collision theory for reactions of atoms having a very high initial energy. Using this theory and certain experimental data, it is concluded that hot hydrogen atoms react to combine with organic molecules at very high collision efficiency (of the order of approximately 0.2 to 0.4) in the energy range 3–10 ev. There is no indication that collisions at much higher energies lead to combination. With most systems, e.g. alkanes, a wide variety of reactions is observed. The systematics of these hot reactions is discussed and evidence on their detailed mechanism is presented. It appears that most products are formed by a fast displacement of an atom or group by the hot hydrogen. There is no evidence for the formation of a common, internally equilibrated, collision complex which decays on a statistic...