Giant Resonances in Atoms, Molecules, and Solids

Transcription

1 Giant Resonances in Atoms, Molecules, and Solids

2 NA TO ASI Series Advanced Science Institutes Series A series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences B Physics C Mathematical and Physical Sciences o Behavioral and Social Sciences E Engineering and Materials Sciences F Computer and Systems Sciences G Ecological Sciences H Cell Biology Plenum Publishing Corporation New York and London D. Reidel Publishing Company Dordrecht, Boston, and Lancaster Martinus Nijhoff Publishers The Hague, Boston, Dordrecht, and Lancaster Springer-Verlag Berlin, Heidelberg, New York, London, Paris, and Tokyo Recent Volumes in this Series Volume 150-Particle Physics: Cargese 1985 edited by Maurice Levy, Jean-Louis Basdevant, Maurice Jacob, David Speiser, Jacques Weyers, and Raymond Gastmans Volume 151-Giant Resonances in Atoms, Molecules, and Solids edited by J. P. Connerade, J. M. Esteva, and R. C. Karnatak Volume 152-0ptical Properties of Narrow-Gap Low-Dimensional Structures edited by C. M. Sotomayor Torres, J. C. Portal, J. C. Mann, and R. A_ Stradling Volume 153-Physics of Strong Fields edited by W. Greiner Volume 154-Strongly Coupled Plasma Physics edited by Forrest J. Rogers and Hugh E. Dewitt Volume 155-Low-Dimensional Conductors and Superconductors edited by D. Jerome and L. G. Caron Volume 156-Gravitation in Astrophysics: Cargese 1986 edited by B. Carter and J. B. Hartle Series B: Physics

3 Giant Resonances in Atoms, Molecules, and Solids Edited by J. P. Connerade Imperial College London, England and J. M. Esteva and R. C. Karnatak University of Paris Orsay, France Springer Science+Business Media, LLC

4 Proceedings of a NATO Advanced Study Institute on Giant Resonances in Atoms, Molecules, and Solids, held June 16-26, 1986, in Les Houches, France Library of Congress Cataloging in Publication Data NATO Advanced Study Institute on Giant Resonances in Atoms, Molecules, and Solids (1986: Les Houches, Haute-Savoie, France) Giant resonances in atoms, molecules, and solids. (NATO ASI series. Series B, Physics; v. 151) "Proceedings of a NATO Advanced Study Institute on Giant Resonances in Atoms, Molecules, and Solids, held June 16-26,1986, in Les Houches, France" T.p. verso. "Published in cooperation with NATO Scientific Affairs Division." Includes bibliographical references and index. 1. Nuclear magnetic resonance, Giant Congresses. 2. Atomic theory Congresses. 3. Molecular spectra Congresses. 4. Solids Spectra Congresses. 5. Atomic spectra Congresses. I. Connerade, J. P. II. Esteva, J. M. III. Karnatak, R. C. IV. Title. V. Series. QC762.N / ISBN Springer Science+Business Media New York 1987 Originally published by Plenum Press, New York in 1987 Softcover reprint of the hardcover 1st edition 1987 All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher ISBN ISBN (ebook) DOI /

5 FOREWORD Often, a new area of science grows at the confines between recognised subject divisions, drawing upon techniques and intellectual perspectives from a diversity of fields. Such growth can remain unnoticed at first, until a characteristic fami ly of effects, described by appropriate key words, has developed, at which point a distinct subject is born. Such is very much the case with atomic 'giant resonances'. For a start, their name itself was borrowed from the field of nuclear collective resonances. The energy range in which they occur, at the juncture of the extreme UV and the soft X-rays, remains to this day a meeting point of two different experimental techniques: the grating and the crystal spectrometer. The impetus of synchrotron spectroscopy also played a large part in developing novel methods, described by many acronyms, which are used to study 'giant resonances' today. Finally, although we have described them as 'atomic' to differentiate them from their counterparts in Nuclear Physics, their occurrence on atomic sites does not inhibit their existence in molecules and solids. In fact, 'giant resonances' provide a new unifying theme, cutting accross some of the traditional scientific boundaries. After much separate development, the spectroscopies of the atom in various environments can meet afresh around this theme of common interest. Centrifugal barrier effects and 'giant resonances' proper emerged almost simultaneously in the late 1960's from two widely separated areas of physics, namely the study of free atoms and of condensed matter. It soon became apparent that the features later to be described as 'giant resonances' form a unique class of excitations which preserve their character under many changes of environment from the free atom right through to the solid. The effects of the molecular field on the 'giant resonances' were then explored. Thus, the interdisciplinary nature of the subject was actually exploited from the outset as one means of characterising this class of resonances. A further thread winds through the theory of atomic centrifugal effects. Within the independent particle model, the connection between 'giant resonances' and the lanthanide contraction became apparent, uncovering a rich complexity of related phenomena. Thanks to this connection, the subject of 4f electrons, their occupancy and their remarkable v

6 hesitations of valence in condensed matter were perceived in a new light by atomic physicists. Indeed, a quasi-periodic table, obtained semi-empirically from studies of conductivity and magnetism in solids, charts a sophisticated relation bet.ween localisation and the nature of the atom, the precise details of which remain to be accounted for. This table is perhaps a central piece of the new subject area. From a theoretical standpoint, many fundamental issues have arisen in this general area of science. Taking atomic 'giant resonances' first, the inadequacy of the simple independent particle approximations led to the furtherance of many-body theories (the random phase approximation with exchange and many body perturbation theory), to the development of density functional approaches for the calculation of atomic spectra and, indeed, to the refinement of the independent particle pictures themselves, which now include term-dependent Hartree-Fock potentials for the continuum states, incorporating some essential aspects of the more complete theories. An even more fundamental advance exploits a static mean central field optimised according to the prescription of relativistic quantum field theory for N-electron systems - the so-called g-hartree equation, which has proved remarkably successful in treating wavefunction collapse. There are few problems as fundamental in low energy physics as the study of many-body phenomena in a quantum system with few particles (the atom). Thus, basic issues of wide significance have been raised. In molecular physics, several kinds of very broad resonances occur. The simplest to characterise is the atomic 'giant resonance' slightly modified by molecular bonds (as in e.g. LaF 3 ). Next come 'giant resonances' which closely mimick those in a corresponding united atom (as e.g. in HI). Finally, there are resonances of similar type in large molecules, which exist only by virtue of the molecular field and have no direct analogue in atoms. All these types of resonances are being actively explored, and their nature is currently a subject of discussion. Passing from molecules to chemistry, photon stimulated desorption from surfaces can be resonantly enhanced by tuning to 'giant resonances'. This provides a new means of probing adsorption, as well as an intriguing class of new effects. The subject of centrifugal barriers and its connection with the quasi-periodic table mentioned above could provide new insights into rare-earth catalysis. In condensed matter, there is the challenge of wedding Anderson-type models with atomic structure theory: the former are highly successful in describing 4f occupancies and interrelating different spectroscopies, while the latter is necessary to account for the persistence of multiplet structure in solids. A unified theory would clearly be an important achievement. There are also connections between 'giant resonances' and laser-based research which were explored in les Houches. First, the 'giant resonances' are closely related to certain unresolved transition arrays in the spectra of laser-produced vi

7 rare-earth plasmas. Secondly, collective effects can actually be driven directly by an intense laser field, and this is a novel area of research in its own right. Against this backcloth of activity in the study of resonant wavefunction localisation, it seemed opportune to hold an interdisciplinary NATO Advanced Study Institute on 'Giant Resonances in Atoms Molecules and Solids'. Most researchers in the field had not had the opportunity to pursue extensive contacts with colleagues from quite different, though related, disciplines, and the subject was in some danger of becoming fragmented. There are few areas of scientific research which combine such breadth and richness of practical applications with a truly fundamental nature. We have studiously avoided, in this preface, any attempt at defining 'giant resonances' and how one mayor may not distinguish them from shape resonances. Authors differ on this issue, and several attempts at answering this question will be found in the present volume. Of course, we have our opinions on the matter, and the reader is encouraged to form his own judgement. Suffice it to say that this was a matter of hot debate between proponents and adversaries of the many-body approaches. The present Proceedings provide, we believe, a comprehensive pedagogical account of the subject of 'giant resonances' in which the reader will find detailed discussion of all the issues raised above. Since the area is evolving rapidly, the articles collected here may require updating fairly soon in their more technical aspects. However, we hope their pedagogical nature will be durable, and will make the present volume a valuable introduction to this new field for some time to come. J.P. Connerade J.M. Esteva R.C. Karnatak vii

8 CONTENTS I. ATOMIC THEORY AND EXPERIMENTS Al. Controlled Collapse and the Profiles of "Giant Resonances" 3 J.P. Connerade A2. Mayer-Fermi Theory and the Long Sequences in the 25 Periodic Table D.C. Griffin, Robert D Cowan, M.S. Pindzola A3. Relativistic Correlations in Atoms 49 K. Dietz A4. Atomic Many Body Theory of Giant Resonances 71 Hugh P. Kelly and Zikri Altun A5. Giant Resonances in Atoms and in Fluorine Cage 91 Molecules M.W.D. Mansfield A6. Giant Resonances in the 4d Subshell Photoabsorption 115 Spectra of Sa, Ba+, and Ba++ K. Nuroh, E. Zaremba and M.J. Stott A7. Giant Resonances in the Transition Regions of the 137 Periodic Table C.W. Clark and T.B. Lucatorto AS. Giant Resonances in Heavy Elements: Open-shell 153 Effects, Multiplet Structure and Spin - Orbit Interaction F r a n ~ Combet-Farnoux o i s e A9. Giant Resoanaces as a Probe of Collective Excitations 171 in Atoms and Solids G. Wendin Al0. The State-Specific Theory of Atomic Structure and 213 Aspects of the Dynamics of Photoabsorption C.A. Nicolaides Al1. Influence of Centrifugal Barrier Effects on the 225 Autoionising Resonances M.A. Baig, K. Sommer, J.P. Connerade, J. Hormes ix

9 A12. Giant Resonance Phenomena in the Electron Impact Ionization of Heavy Atoms and Ions S.M. Younger A13. The g-thomas-fermi Method Th. Millack and G. Weymans A14. The Giant Resonances in the 3d Transition Elements: 247 Single and Double Photoionization in the Region of the 3p Excitation M. Schmidt and P. Zimmermann A15. Decay Channels of Core Excitation Resonances in Atomic 251 Lanthanides and 3rd Transition Metals M. Meyer, Th. Prescher, E.v. Raven, M. Richter, E. Schmidt, B. Sonntag and H.E. Wetzel II. MOLECULES - THEORY AND EXPERIMENTS M1. Inner Shell Resonances in Molecular Photoionization I. Nenner M2. Resonances in the K-Shell Spectra of Fluorinated Organic Molecules A.P. Hitchcock, P. Fischer and R. McLaren M3. Atomic Autoionization Observed in nd 0* Molecular Resonances P. Morin M4. Are the d-f shape Resonances in Diatomic Molecules "Giant Resonances"? H. Lefebvre-Brion III. SOLIDS - THEORY AND EXPERIMENTS 51. The Quasi-Periodic Table and Anomalous Metallic 311 Properties A.M. Boring and J.L. Smith 52. A Condensed Matter View of Giant Resonance Phenomena 321 Andrew Zangwi Photon and Electron - Stimulated Desorption from 339 Rare Earth Oxides G.M. Loubriel 54. Applications of Electron Energy Loss Spectroscopy to 353 Giant Resonances in Rare Earth and Transition Metal Systems J.A.D. Matthew S5. High Resolution Soft X-Ray Spectra of d-f Transitions: 361 New Specific Features in the 3d Resonances of Ce0 2, PrO. and Tb0 2 J-M Esteva and R.C. K a r n a ~ a k x

10 S6. The Effects of 4f Level Occupancy, Coulomb Interactions, 381 and Hybridization on Core Level Spectra of Lanthanides J.C. Fuggle S7. Intermediate Valence Spectroscopy 405 O. Gunnarsson and K. Schonhammer 58. Resonant Photoemission using the d-f Giant Resonances J. Oh S9. Mixed Electronic States and Magnetic Moments Studied 447 with near Edge X-Ray Absorption Spectroscopy G. van der Laan S10. Photoelectron Spectroscopic Observation of the Density 463 of Low-Lying Excitations in Ce-Solids W.O. Schneider, F. Patthey, Y. Baer, B. Delley Sll. The 4d - 4f Giant Resonances from Barium through the 473 Rare-Earths U. Becker S12. Appearance-Potential Study of Resonant Transitions in 483 Lanthanides D.R. Chopra S13. On the Excitation and Relaxation of 5p Electrons near 491 Threshold in Eu and Yb Metals G. Rossi IV. LASERS AND PLASMAS L1. The Spectra of Laser Produced Plasmas with Lanthanide 505 Targets G. 0' Sull ivan L2. Ordered Many-Electron Motions in Atoms and X-Ray Lasers 533 C.K. Rhodes Useful Acronyms Participants Author Index Subject Index xi