Principles and Applications of ESR Spectroscopy

Transcription

1 Principles and Applications of ESR Spectroscopy

2 Anders Lund Masaru Shiotani Shigetaka Shimada Principles and Applications of ESR Spectroscopy 123

3 Prof. Anders Lund Department of Physics, Chemistry and Biology, IFM Linkoping University The Emeritus Academy, Linkoping University SE , Linkoping Sweden Prof. Masaru Shiotani Graduate School of Engineering Hiroshima University Takamigaoka, Takaya Higashi-Hiroshima Japan Prof. Shigetaka Shimada Graduate School of Engineering Nagoya Institute of Technology Midorigaoka Midori-Machi Owari-Asahi Japan ISBN e-isbn DOI / Springer Dordrecht Heidelberg London New York Springer Science+Business Media B.V No part of this work 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, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed on acid-free paper Springer is part of Springer Science+Business Media (

4 Preface ESR or Electron Spin Resonance is a spectroscopic method for studies of paramagnetic species. Species of this kind are of interest both from fundamental viewpoints and for a broad range of applications in materials and polymer sciences, physical chemistry and chemical physics, bio-chemistry and medicine, catalysis and environmental sciences, radiation dosimetry and geological dating, as well as radiation physics and chemistry. The magnetic properties, mainly attributed to the electron spin, can be employed to determine both the structure (at a molecular level) and the amount of paramagnetic species in a sample with the ESR method. This method has been presented from different viewpoints in the past. Previous monographs on ESR spectroscopy have focused on the technique as such, while the general textbooks in physics, chemistry or spectroscopy only briefly explain the applications, which are mainly presented in specialist reviews and in the original literature. The present book is based upon the authors long experience of teaching the subject to a mixed audience, with backgrounds ranging from physics to biology. It aims both at providing the principles of continuous wave and pulsed ESR techniques and to illustrate the potential of the method by examples of applications. The principles of ESR, multi-resonance and pulsed ESR methods, the analysis of spectra, and multifrequency and high field ESR techniques treated in the first four chapters are thus followed by five chapters exemplifying recent applications in molecular science, in catalysis and environmental science, in polymer science, in spin labeling and molecular dynamics, and in quantitative ESR. Theoretical derivations are in general left out, as they are presented repeatedly in previous works. The necessary theory is instead illustrated by practical examples from the literature. Commonly used computer codes to evaluate experimental ESR data are described with examples. Internet addresses to download the software are given, whenever possible. Formulae employed in those programs are reproduced in appendices, when the original literature references are not easily available. The theory and the application parts are to a large extent independent of each other to allow study of a special subject. For reasons of easy access of data and diagrams several examples from the authors own work were employed to illustrate certain applications. Exercises included in the theoretical part are mainly concerned with spectra interpretations, as this is the key issue in the analysis of experimental data. v

5 vi Preface Our intention has been to prepare a textbook with the following issues in mind: 1. The book Principles and applications of ESR spectroscopy is for students and scientists planning to use the method without necessarily becoming experts. The book provides sufficient knowledge to properly apply the technique and to avoid mistakes in the planning and performance of the measurements. 2. The theoretical part is adapted for a non-specialist audience. Derivations of wellknown formulae are left out. The non-specialist does not want the derivations, while the physicist does not need them. The necessary theory is instead illustrated by practical examples from the literature. The potential of the method is demonstrated with applications selected from the authors wide experience. 3. Commonly used software to evaluate experimental ESR data is described with examples. Addresses to download the software are given. Linköping, Sweden Higashi-Hiroshima, Japan Owari-Asahi, Japan Anders Lund Masaru Shiotani Shigetaka Shimada

6 Contents Part I Principles 1 Principles of ESR Introduction Paramagnetism Which Substances Are Paramagnetic? Resonance Relaxation Saturation Hyperfine Structure Fine Structure or Zero-Field Splitting Quenching of Orbital Angular Momentum Instrumentation SpinDistribution IsotropicCoupling AnisotropicCoupling AnExample Complex Spectra Units,ConstantsandSymbolsinESR Historical and Modern Developments High Frequency ENDOR Short-Lived Radicals PulsedESR Summary References Exercises Multi-Resonance and Pulsed ESR Introduction ENDOR ENDOR in Liquids ENDOR in Single Crystals ENDOR in Disordered Solids vii

7 viii Contents 2.3 PulsedESR PulsedESRinSolution PulsedESRinSolids Pulsed ENDOR RelaxationTimes Distance Measurements ThePoint-DipoleApproximation Electron-Electron Distances Electron-Nucleus Distances Summary Appendix References Exercises Analysis of Spectra Introduction Liquids Hyperfine Couplings EquivalentNuclei Inequivalent Nuclei Large Hyperfine Couplings Multi-Component Spectra Software The g-factor Analysis of Single Crystal Spectra The Schonland Method The g-tensor Sites The Hyperfine and Nuclear Quadrupole Coupling Tensors The Zero-Field Splittng Combined Zero-Field and Hyperfine Couplings SoftwareforSingleCrystalAnalysis Analysis of Powder Spectra ESR Powder Spectra ENDOR Powder Spectra ESEEM Powder Spectra Summary Appendices References Exercises Multi-Frequency and High Field ESR Introduction g-factorresolution Resolution of Apparent Isotropic or Axially Symmetric g-tensor

8 Contents ix Resolution of g-tensor in Presence of Hyperfine Structure (hfs) Zero-Field Splitting (zfs) Zero-Field Splitting in Powder Spectra Deviations from First Order Appearance Sign of Zero-Field Splitting Hyperfine Couplings (hfc) TheDirectFieldEffect Sign of Anisotropic Hyperfine Couplings Magnetically Coupled Systems S = ½Dimers Other Coupled Systems Multifrequency ENDOR and ESEEM Summary Appendix References Exercises Part II Applications of ESR 5 Applications to Molecular Science Introduction RadicalAnions Perfluorocycloalkane Radical Anions: Electron Delocalization Perfluoroalkene Radical Anions: Structural Distortion AcetyleneRadicalAnions:Trans-BentStructure RadicalCations Jahn-Teller Distortion of T d and D 3h Molecules D-Labelled Methane Radical Cations: CH + 4, CDH + 3,CD 2 H + 2,CD 3 H + and CD Trimethylenemethane Radical Cation High Resolution ESR Spectra and Quantum Effects D-Labelled Methyl Radicals: Nuclear Spin-RotationCouplings Hydrogen Atom Methyl Radical Pairs Hydrogen Atom Hydrogen Molecule Complex Hydrogen Molecular Complex Ions of H 6-n D + n in para-h 2 Matrix Summary Appendices References Applications to Catalysis and Environmental Science Introduction Surface Probing: Nitric Oxide Interactions with Metal Ions in Zeolites

9 x Contents NO-Na + Complex Formed in Zeolites Triplet State of (NO) 2 Bi-Radical Formed in Zeolite Other Nitrogen Oxides as Spin Probes Cu(I)-NO Complexes Formed in Zeolites Multifrequency ESR Spectra Pulsed ENDOR and HYSCORE Studies Molecular Motion Probes: Radicals in Zeolites Structure and Dynamics of Et 3 N + and Pr 3 N + in AlPO Cage Effects on Stability and Molecular Dynamics of Amine Radicals in Zeolites Titanium Dioxide (TiO 2 ) Semiconductor Photocatalysis Nitrogen-Doped TiO Reversible Photoinduced Electron Transfer in TiO 2 (Rutile) Electron Transfer in Mixed Phase of Anatase and Rutile Superoxide (O 2 )IonRadical g-values of O OLabelingStudy Summary Appendices References Applications to Polymer Science Introduction What Can We Obtain from the ESR Parameters and Their Changes in Polymer Materials? Polymerization Mechanism RadicalPolymerizationintheLiquidState RadicalPolymerizationintheSolidState Radical Polymerization of Macro-Monomers Radiation Effects: Radiation Physics and Chemistry ofpolymermaterials Free Radicals Produced by Irradiation of Polymers withionizing Radiation Decay of Free Radicals Produced by γ-irradiation ofpolymers Free Radical Pairs Produced by Irradiation of PolymerswithIonizingRadiation Inhomogeneous Spur-Like Trapping of Free Radicals by Irradiation of Polymers with Ionizing Radiation Mechanical Destruction of Solid Polymers Free Radicals Produced by Mechanical Destruction of Solid Polymers: Mechano-Radicals High Chemical Reactivity of Mechano-Radicals High Molecular Mobility of Mechano-Radicals

10 Contents xi 7.6 Auto-Oxidation Mechanisms of Polymer Systems ESR Spectrum of Peroxy Radicals in Polymer Matrices Oxidation Processes in Irradiated Polymers and ChemicalReactionsofPeroxyRadicals Structure and Molecular Motion of Peroxy RadicalsinPolymerMatrices Conducting Polymers Diffusive Motion of the Soliton in Pristine Polyacetylene Detected by the ESR Line Width Spin Density Distribution of the Soliton in Pristine Polyacetylene Detected by ENDOR Dyson s Theory of ESR Line Shapes in Metals ESR Spectra of Pristine and AsF 5 Doped Polyacetylene (PA) Summary Appendices References Spin Labeling and Molecular Dynamics Introduction Molecular Motion in Solid Polymers Characteristics of ESR for Studying Molecular MotioninSolidPolymers Evaluation of Correlation Time for Molecular Motion from ESR Spectra Glass-Rubber Transition Detected by the Spin Label Method for Polystyrene (PS): Molecular Weight Dependence Glass-Rubber Transition Detected by the Spin Label Method for Polyethylene (PE): Crystallinity Dependence Glass-Rubber Transition Detected by the Spin ProbeMethod Molecular Mobility of an Amorphous Chain in the Crystallization Process Applications of Spin Labeling Method to Biopolymer Systems StructureofBiologicalCellMembrane Fluidity of Biological Membranes and the Order ParameterofaLipidChain Dependence of Molecular Mobility of Lipid Bilayers on Position of the Methylene Group Lateral Phase Separation in Phospholipid Membranes Caused by Lateral Diffusion of Lipid Chains Lipid-Protein Interactions and Rotational Diffusion Summary References

11 xii Contents 9 Applications of Quantitative ESR Introduction Absolute Concentration Measurements Reference Samples Accuracy Line Shapes ESRDosimetry TheAlanineESRDosimeter NewMaterialsforESRDosimetry ESRImagingofRadiationDose ESRDating AdditiveDoseMethod IrradiatedFoodandRadiationProcessedMaterials Microwave Saturation Properties Summary Appendix References General Appendix G Index