Positron Annihilation in Chemistry

Abstract

© Springer-Verlag Berlin Heidelberg 1995 Softcover reprint of the hardcover I st edition 1995The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.Typesetting: Macmillan India Ltd, Bangalore-25 SPIN: 10069941 54/3140/SPS -5 432 I 0 -Printed on acid-free paper PrefaceThe electron, positron, and positronium (Ps, the electron-positron bound state) are the only light particles which participate in normal low-energy processes of physics and chemistry. Because of their small masses quantum mechanical phenomena play a great role in their behavior. Good accounts of the excess electron behavior are available. Similarly, several good books treat the behavior of the positron in solid state and gas physics. However, the research on the positron and Ps in chemistry-oriented fields of science is not well treated in the literature. In liquids Ps is normally in the "bubble" state, and hence, its chemical reactions are very exceptional, indeed. The states and reactions of the positron in insulating liquids can profitably be compared to those of the only other charged light particle, the excess electron. Furthermore, Ps is formed by a reaction between the positron and excess electron in the positron spur, and Ps formation studies give, therefore, information on excess electrons, too. Consequently, to understand "light particle chemistry" it is necessary to have a good understanding of the chemistry of the positron and Ps. This book is a critical review of the research on the behavior of the positron and Ps performed within chemistry-oriented positron annihilation. In particular, I have emphasized the interpretation of selected, typical, experimental results in the field. The book does not give an exhaustive discussion of all the published results. This is impossible because of lack of space anyway. Discussions of experimental results and theoretical explanations believed to be outdated, erratic, or misleading are mainly omitted, with the exceptions of those which have been used extensively in the literature. The omission of certain works might just indicate that the accepted ideas and concepts in the field have changed very much recently.Partly because of lack of space positron annihilation in several fields on the borderline of chemistry, physics, and/or materials science is not discussed. For example, research on metals, semiconductors, ionic crystals, ceramic materials, high Tc superconductors, gases, and liquid noble gases is not discussed, except if the results are of general interest.The writing of this book would have been impossible without many years of very good collaboration with M. Eldrup and N.J. Pedersen at Risoe. Furthermore, I spent seven months doing fruitful work at IMFUFA, Roskilde University VI Preface

Positronium Formation in Organic Liquids

“…1 for the latter. Presently derived lifetimes (τ 2 = 380−460 ps for all the three compounds) and intensities I 2 and I 1 at room temperature agree within uncertainties with three and four-component analysis of Consolati and co-workers [23,24] and Mogensen [15]. All these data suggest that paramagnetic quenching has no influence either on the very o-Ps formation or on the other annihilation routes.…”

“…Nowadays novel coincidence systems allow to resolve at least three different annihilation routes in organic liquids and solids. Some authors report even fourcomponent analysis [15,16]. Despite these trends, there are no quantitative data about O 2 influence on the behaviour of other annihilation channels -different from the pick-off process of o-Ps.…”

Amorphous-amorphous transition in glassy polymers subjected to cold rolling studied by means of positron annihilation lifetime spectroscopy

“…On the other hand, o-Ps has a lifetime in vacuum of 140 ns that is strongly reduced in polymers to few nanoseconds depending on the free-volume properties of the sample. 15 In particular, the measured o-Ps lifetime is related to the size of the free-volume cavity using the following semiempirical equation: 16 o-Ps = 1…”

Hierarchical Porosity in Self‐Assembled Polymers: Post‐Modification of Block Copolymer–Phenolic Resin Complexes by Pyrolysis Allows the Control of Micro‐ and Mesoporosity

“…PALS is a powerful in situ probe for characterization of porous materials and is applicable to sizes from sub-nanometer to nanometer scale. [44][45][46] In this method, the obtained ortho-positronium (o-Ps) pick-off annihilation lifetime (s 3 ) is directly related to the mean free-volume (micropore) size, and its intensity (I 3 ) is often interpreted to reflect the micropore volume density (see Experimental for more information about PALS). [47,48] Figure 5a and b shows the plot of s 3 and I 3 as a function of pyrolysis conditions.…”