Editor's Preface ................................................. 9 Authors' Preface ................................................ 11 1 Introduction .................................................. 13 1.1 Radical pairs and their reactions ....................... 13 1.2 Mechanisms of RP singlet-triplet transitions ............ 16 1.3 The origin of CIDNP and magnetic effects in radical reactions ....................................... 22 1.4 Basic steps of investigations ........................... 29 2 The theory of radical recombination ........................... 32 2.1 The dynamics of molecular motions in solutions and the spin-independent theory of radical recombination .... 32 2.1.1 The statistics of radical encounters in solutions ...................................... 32 2.1.2 Radical recombination .......................... 45 2.2 RP singlet-triplet evolution ............................ 57 2.2.1 Spin dependence of RP recombination ............ 58 2.2.2 The spin-Hamiltonian and the equation of motion of RP spins ............................. 61 2.2.3 RP spin dynamics in high magnetic fields ....... 65 2.2.4 RP spin dynamics in low magnetic fields ........ 72 2.2.5 RP spin dynamics under random hf modulation .... 89 2.2.6 RP spin dynamics in microwave fields ........... 93 2.3 Mathematical tools of the theory ........................ 96 2.3.1 Kinetic equations of RP geminate recombination 98 2.3.2 Radical recombination in homogeneous solutions 106 2.3.3 The method of summation of RP re-encounter contributions to the recombination ............ 110 2.3.4 Methods of approximate calculations ........... 113 3 The theory of magnetic effects in radical reactions .......... 117 3.1 Radical recombination in high magnetic fields .......... 117 3.1.1 The continuous diffusion model ................ 118 3.1.2 The reaction equilibrium ...................... 124 3.1.3 Exchange interaction effects .................. 125 3.1.4 Radical diffusion by jumps .................... 128 3.1.5 Recombination in the presence of radical acceptors ..................................... 131 3.1.6 Recombination of radicals with anisotropic reactivity .................................... 132 3.1.7 Radical-ion recombination ..................... 134 3.1.8 The exponential model ......................... 136 3.1.9 S-T+, T- transitions in high magnetic fields .......................... 138 3.1.10 The relaxation mechanism of S-T transitions ... 140 3.1.11 Sequence of radical pairs ..................... 142 3.1.12 Triplet RP recombination ...................... 146 3.2 Radical recombination in low magnetic fields ........... 147 3.2.1 The relation between different RP recombination probabilities ................... 148 3.2.2 One-nucleus radical pairs with spin I=1/2 ..... 149 3.2.3 Other model systems ........................... 157 3.2.4 The semi-classical theory of magnetic effects in the recombination of radicals with a large number of magnetic nuclei ..................... 159 3.3 The magnetic isotope effect ............................ 162 3.3.1 Qualitative considerations .................... 163 3.3.2 Magnetic isotope effect in zero magnetic field 163 3.3.3 Field dependence of the magnetic isotope effect 165 4 The theory of chemically induced dynamic nuclear and electron spin polarizations .................................. 168 4.1 Phenomenological description and spectroscopic manifestation of CIDNP and CIDEP ....................... 168 4.1.1 Net polarization effects ...................... 168 4.1.2 Multiplet polarization effects ................ 170 4.2 CIDNP theory for high magnetic fields ................... 172 4.2.1 Basic regularities of net CIDNP effects ....... 172 4.2.2 Basic regularities of multiplet CIDNP effects 174 4.2.3 The Kaptein rules for CIDNP effects ........... 175 4.2.4 The operator formalism in CIDNP theory ........ 176 4.2.5 Quantitative CIDNP calculations; absolute values of nuclear polarization ................ 179 4.2.6 The influence of radical acceptors on CIDNP ... 187 4.2.7 The influence of anisotropic radical reactivity on CIDNP ........................... 187 4.2.8 RP substitution ............................... 190 4.2.9 CIDNP kinetics ................................ 196 4.2.10 Concluding remarks ............................ 199 4.3 Low field CIDNP theory ................................. 199 4.3.1 Qualitative considerations .................... 199 4.3.2 CIDNP effects in short-lived RPs .............. 206 4.3.3 Approximate calculations ...................... 210 4.3.4 Precise calculations .......................... 213 4.4 CIDNP in biradical reactions ........................... 217 4.5 CIDEP theory in radical pairs .......................... 224 4.6 Spin polarizations in triplet molecule reactions ....... 235 5 Experimental observations of magnetic field effects in radical reactions ............................................ 243 5.1 Spin effects ........................................... 243 5.2 Reactions of neutral radicals .......................... 245 5.3 Recombination of radical-ions .......................... 255 5.4 Optical detection of radical-ion pair ESR spectra ...... 269 5.5 Radical reactions in solids ............................ 276 5.6 Biochemical reactions .................................. 277 5.7 Processes involving triplet molecules .................. 281 5.8 Conclusion ............................................. 288 6 Magnetic isotope effect ...................................... 291 6.1 Introduction ........................................... 291 6.2 Reactions of neutral radicals .......................... 292 6.3 Reactions of radical-ions .............................. 298 6.4 Conclusion ............................................. 298 7 Chemically induced dynamic nuclear polarization .............. 300 7.1 Experimental observations and detection of CIDNP ....... 300 7.1.1 High magnetic fields .......................... 300 7.1.2 Low magnetic fields ........................... 304 7.2 Experimental basis of the CIDNP theory ................. 307 7.2.1 High magnetic fields .......................... 307 7.2.2 Low magnetic fields ........................... 320 7.3 Chemical applications of CIDNP ......................... 328 7.3.1 Identification of radical stages .............. 328 7.3.2 Radical transformation genealogy .............. 330 7.3.3 CIDNP kinetics ................................ 332 7.3.4 Radical and nonradical reaction routes ........ 332 7.3.5 Identification of crypto-radical pathways ..... 342 7.3.6 Identification of unstable intermediates ...... 345 7.3.7 Fast reaction kinetics in radical pairs ....... 348 7.3.8 "Hot radicals" ................................ 358 7.3.9 CIDNP applications in structural chemistry .... 360 7.3.10 Chemical applications of low field CIDNP ...... 369 7.4 CIDNP in the gas phase ................................. 373 7.4.1 CIDNP in biradical reactions .................. 373 7.4.2 CIDNP in radical-ion reactions ................ 375 7.5 CIDNP in biradicals .................................... 376 7.6 Technical applications of CIDNP ........................ 379 7.6.1 Nuclear magnetometry .......................... 379 7.6.2 Oriented polarized targets .................... 380 7.6.3 Radio-frequency generation with chemical pumping (chemical RASER) ...................... 380 7.7 CIDNP detected magnetic resonance ...................... 383 8 Chemically induced dynamic electron polarization ............. 387 8.1 Experimental methods of CIDEP observation and analysis 387 8.2 Experimental CIDEP investigations ...................... 389 8.2.1 CIDEP in radical pairs ........................ 390 8.2.2 CIDEP in reactions of triplet molecules ....... 396 8.3 Conclusion ............................................. 401 References ..................................................... 403 Subject index .................................................. 417