Publication Date:
2015-03-05
Description:
Momentum distributions associated with ortho -positronium ( o -Ps) pick-off annihilation photon are often influenced by light elements, as, e.g., carbon, oxygen, and fluorine. This phenomenon, so-called element specificity of o -Ps pick-off annihilation, has been utilized for studying the elemental environment around the open spaces. To gain an insight into the element specificity of o -Ps pick-off annihilation, the chemical shift of oxygen 1 s binding energy and the momentum distributions associated with o -Ps pick-off annihilation were systematically investigated for alkali-metal loaded SiO 2 glasses by means of X-ray photoelectron spectroscopy and positron-age-momentum correlation spectroscopy, respectively. Alkali metals introduced into the open spaces surrounded by oxygen atoms cause charge transfer from alkali metals to oxygen atoms, leading to the lower chemical shift for the oxygen 1 s binding energy. The momentum distribution of o -Ps localized into the open spaces is found to be closely correlated with the oxygen 1 s chemical shift. This correlation with the deepest 1 s energy level evidences that the element specificity of o -Ps originates from pick-off annihilation with orbital electrons, i.e., dominantly with oxygen 2 p valence electrons and s electrons with lower probability.
Print ISSN:
0021-9606
Electronic ISSN:
1089-7690
Topics:
Chemistry and Pharmacology
,
Physics
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