Electron Spin Resonance Elementary Theory and Practical Applications by John Wertz , Springer

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Springer Electron Spin Resonance Elementary Theory and Practical Applications by John Wertz

In the twenty-five years since its discovery by Zavoiskii, the technique of electron spin resonance (ESR) spectroscopy has provided detailed struc tural information on a variety of paramagnetic organic and inorganic sys tems. It is doubtful that even much later than 1945 any chemist would have been so bold as to predict the great diversity of systems which have proved amenable to study by ESR spectroscopy. In this book we have attempted to provide numerous examples of actual ESR spectra to illus trate the wide scope of application. No attempt has been made to present a comprehensive coverage of the literature in any field, but references to reviews and key articles are given throughout the book. This introductory textbook had its origin in lecture notes prepared for an American Chemical Society short course on electron spin resonance. The present version is the result of extensive revision and expansion of the original notes. Experience with such courses has convinced us that there are large numbers of chemists, physicists, and biologists who have a strong interest in electron spin resonance. The mathematical training of most of the short-course students is limited to calculus. Their contact with theories of molecular structure is largely limited to that obtained in an elementary physical chemistry course. It is to an audience of such background that this book is directed._x000D_ Table of contents :- _x000D_ 1 Basic Principles of Electron Spin Resonance.- 1-1 Introduction.- 1-2 Energy of Magnetic Dipoles in a Magnetic Field.- 1-3 Quantization of Angular Momentum.- 1-4 Relation between Magnetic Moments and Angular Momenta.- 1-5 Interaction of Magnetic Dipoles with Electromagnetic Radiation.- 1-6 Characteristics of the g Factor.- Problems.- 2 Basic Instrumentation of Electron Spin Resonance.- 2-1 A Simple ESR Spectrometer.- 2-2 Choice of Experimental Conditions.- 2-3 Typical Spectrometer Arrangement.- 2-3a The Cavity System.- 2-3b The Source.- 2-3c The Magnet System.- 2-3d The Modulation and Detection Systems.- 2-4 Line Shapes and Intensities.- References.- Problems.- 3 Nuclear Hyperfine Interaction.- 3-1 Introduction.- 3-2 Origins of the Hyperfine Interaction.- 3-3 Energy Levels of a System with One Unpaired Electron and One Nucleus with I = 1/2.- 3-4 The Energy Levels of a System with S = 1/2 and I=1.- 3-5 Summary.- Problems.- 4 Analysis of Electron Spin Resonance Spectra of Systems in the Liquid Phase.- 4-1 Introduction.- 4-2 Energy Levels of Radicals Containing a Single Set of Equivalent Protons.- 4-3 ESR Spectra of Radicals Containing a Single Set of Equivalent Protons.- 4-4 ESR Spectra of Radicals Containing Multiple Sets of Equivalent Protons.- 4-5 Hyperfine Splittings from Other Nuclei with I = 1/2.- 4-6 Hyperfine Splittings from Nuclei with I > 1/2.- 4-7 Useful Rules for the Interpretation of Spectra.- 4-8 Other Problems Encountered in the ESR Spectra of Free Radicals.- 4-9 Second-order Splittings.- Problems.- 5 Interpretation of Hyperfine Splittings in ?-type Organic Radicals.- 5-1 Introduction.- 5-2 Molecular Orbital Energy Calculations.- 5-3 Unpaired Electron Distributions.- 5-4 The Benzene Anion and Its Derivatives.- 5-5 The Anions and Cations of the Polyacenes.- 5-6 Other Organic Radicals.- 5-7 Summary.- References-HMO Method.- Problems.- 6 Mechanism of Hyperfine Splittings in Conjugated Systems.- 6-1 Origin of Proton Hyperfine Splittings.- 6-2 Sign of the Hyperfine Splitting Constant.- 6-3 Extension of the Molecular Orbital Theory to Include Electron Correlation.- 6-4 Alkyl Radicals-A Study of Q Values.- 6-5 The Effect of Excess Charge on the Parameter Q.- 6-6 Methyl-proton Hyperfine Splittings-Hyperconjugation.- 6-7 Hyperfine Splitting by Nuclei Other than Protons.- Problems.- 7 Anisotropic Interactions in Oriented Systems with S = 1/2.- 7-1 Introduction.- 7-2 A Simple Example of Anisotropy of g.- 7-3 Systems with Orthorhombic or Lower Symmetry.- 7-4 Experimental Determination of the g Tensor in Oriented Solids.- 7-5 Anisotropy of the Hyperfine Coupling.- 7-6 Origin of the Anisotropic Hyperfine Interaction.- 7-7 Determination of the Elements of the Hyperfine Tensor.- 7-8 Corrections to Hyperfine Tensor Elements.- 7-9 Line Shapes in Nonoriented Systems.- 7-9a Line Shapes for Systems with Axial Symmetry.- 7-9b Hyperfine Line Shapes for an Isotropic g Factor, S = 1/2 and One Nucleus with I = 1/2.- Problems.- 8 Interpretation of the ESR Spectra of Systems in the Solid State.- 8-1 Generation of Free Radicals in Solids.- 8-2 ?-type Organic Radicals.- 8-2a Identification.- 8-2b Aliphatic Radicals.- 8-2c Radicals from Unsaturated Organic Compounds.- 8-3 ?-type Organic Radicals.- 8-4 Inorganic Radicals.- 8-4a Identification of Radical Species.- 8-4b Structural Information.- 8-5 Point Defects in Solids.- 8-5a Generation of Point Defects.- 8-5b Substitutional or Interstitial Impurities.- 8-5c Trapped-electron Centers.- 8-5d Trapped-hole Centers.- References.- Problems.- 9 Time-dependent Phenomena.- 9-1 Introduction.- 9-2 Spin-lattice Relaxation Time.- 9-3 Other Sources of Line Broadening.- 9-3a Inhomogeneous Broadening.- 9-3b Homogeneous Broadening.- 9-4 Mechanisms Contributing to Line Broadening.- 9-4a Electron Spin-Electron Spin Dipolar Interactions.- 9-4b Electron Spin-Nuclear Spin Interactions.- 9-5 Chemical Line-broadening Mechanisms.- 9-5a General Model.- 9-5b Electron-spin Exchange.- 9-5c Electron Transfer.- 9-5d Proton Exchange.- 9-6 Variation of Linewidths within an ESR Spectrum.- 9-6a Time-dependent Hyperfine Splitting for a Single Nucleus.- 9-6b Time-dependent Hyperfine Splittings for Systems with Several Nuclei.- 9-7 Spectral Effects of Slow Molecular Tumbling Rates.- 9-8 Spectral Effects of Rapid Molecular Tumbling Rates-Spin-rotational Interaction.- 9-9 Summary.- Problems.- 10 Energy-level Splitting in Zero Magnetic Field; The Triplet State.- 10-1 Introduction.- 10-2 The Spin Hamiltonian for S = 1.- 10-3 State Energies for a System with S = 1.- 10-4 The Spin Eigenfunctions for a System with S=1.- 10-5 Electron Spin Resonance of Triplet-state Molecules.- 10-6 Line Shapes for Randomly Oriented Systems in the Triplet State.- 10-7 The "?MS = 2" Transitions.- 10-8 Triplet Ground States.- 10-9 Carbenes and Nitrenes.- 10-10 Thermally Accessible Triplet States.- 10-11 Biradicals; Exchange Interaction.- 10-12 Systems with S > 1.- Problems.- 11 Transition-metal Ions. I..- 11-1 States of Gaseous Transition-metal Ions.- 11-2 Removal of Orbital Degeneracy in Crystalline Electric Fields.- 11-3 The Crystal Field Potential.- 11-4 The Crystal Field Operators.- 11-5 Crystal Field Splittings of States for P-, D- and F-state Ions.- 11-6 Spin-orbit Coupling and the Spin Hamiltonian.- 11-7 D- and F-state Ions with Orbitally Nondegenerate Ground States.- 11-7a D-state Ions 3d1(ttdl + ttgl) in 3d1(cubal + ttgl) 3d7(1s)(oct + ttgl); 3d9(oct + ttgl).- 11-7b F-state Ions 3d8(oct) 3d2(ttdl) 3d8(oct + ttgl) 3d2(ttdl + ttgl) 3d3(oct) 3d7(hs)(ttdl) 3d3(oct + ttgl).- 11-8 S-state Ions 3d5(hs)(oct) 3d5(hs)(oct + ttgl).- Problems.- 12 Transition-metal Ions. II. Electron Resonance in the Gas Phase.- 12-1 Ions in Orbitally Degenerate Ground States.- 12-1a D-state Ions 3d1(oct) 3d1(oct + ttgl), ? > > ? > > ? 3d1(oct + ttgl), ? > > ? ? ? 3d1(oct + trgl) 3d5(1s)(oct + ttgl) 3d9(ttdl + ttgl) 3d6(hs)(oct).- 12-1b F-state Ions 3d2(oct) 3d2(oct + trgl) 3d7(hs)(oct).- 12-1c Jahn-Teller Splitting 3d9(oct) 3d7(1s)(oct).- 12-2 Elements of the 4d and 5d Groups (Palladium and Platinum Groups).- 12-3 The Rare-earth Ions.- 12-4 The Actinide Ions.- 12-5 Deficiencies of the Point-charge Crystal Field Model; Ligand-Field Theory.- 12-6 Electron Resonance of Gaseous Free Radicals.- 12-7 The Practical Interpretation of ESR Spectra of Ions in the Solid State.- Problems.- 13. Double-resonance Techniques.- 13-1 An ENDOR Experiment.- 13-2 Energy Levels and ENDOR Transitions.- 13-3 Relaxation Processes in Steady-state ENDOR.- 13-4 An ENDOR Example: The F Center in the Alkali Halides.- 13-5 ENDOR in Liquid Solutions.- 13-6 ENDOR in Powders and Nonoriented Solids.- 13-7 Electron-electron Double Resonance.- Problems.- 14. Biological Applications of Electron Spin Resonance.- 14-1 Introduction.- 14-2 Substrate Free Radicals.- 14-3 Flavins and Metal-free Flavoproteins.- 14-4 Photosynthesis.- 14-5 Heme Proteins.- 14-6 Iron-sulfur Proteins.- 14-7 Spin Labels.- Appendix A. Mathematical Operations.- A-1 Complex Numbers.- A-2 Operator Algebra.- A-2a Properties of Operators.- A-2b Eigenvalues and Eigenfunctions.- A-3 Determinants.- A-4 Vectors: Scalar, Vector, and Outer Products.- A-5 Matrices.- A-5a Addition and Subtraction of Matrices.- A-5b Multiplication of Matrices.- A-5c Special Matrices and Matrix Properties.- A-5d Dirac Notation for Wave Functions and Matrix Elements.- A-5e Diagonalization of Matrices.- A-6 Tensors.- A-7 Perturbation Theory.- A-8 Euler Angles.- Problems.- Appendix B. Quantum Mechanics of Angular Momentum.- B-1 Introduction.- B-2 Angular-momentum Operators.- B-3 The Commutation Relations for the Angular-momentum Operators.- B-6 Angular-momentum Matrices.- B-7 Addition of Angular Momenta.- B-8 Summary.- Problems.- C-1 The Hamiltonian for the Hydrogen Atom.- C-2 The Spin Eigenfunctions and the Energy Matrix for the Hydrogen Atom.- C-3 Exact Solution of the Determinant of the Energy Matrix (Secular Determinant).- C-4 Selection Rules for High-field Magnetic-dipole Transitions in the Hydrogen Atom.- C-5 The Transition Frequencies in Constant Magnetic Field with a Varying Microwave Frequency.- C-6 The Resonant Magnetic Fields at Constant Microwave Frequency.- C-7 Calculation of the Energy Levels of the Hydrogen Atom by Perturbation Theory.- C-8 Wave Functions and Allowed Transitions for the Hydrogen Atom at Low Magnetic Fields.- Problems.- Appendix D. Experimental Methods; Spectrometer Performance.- D-1 Sensitivity.- D-2 Factors Affecting Sensitivity and Resolution.- D-2a Modulation Amplitude.- D-2b Modulation Frequency.- D-2c Microwave Power Level.- D-2d The Concentration of Paramagnetic Centers.- D-2e Temperature.- D-2g Microwave Frequency.- D-2h Signal Averaging.- D-3 Absolute Intensity Measurements.- Problems.- Table of Symbols.- Name Index._x000D_ show more