Gas-Phase Photoprocesses (Springer Series in Chemical Physics, 123)

This book provides details of the basic frameworks and characteristics of processes occurring in electronically excited states of small molecules, complexes, and clusters. It discusses the perturbations in electronically excited valence states of molecules induced by intramolecular interaction and intermolecular interactions, which occur in collisions and optically populated, weakly bound complexes. Further, it describes the kinetics and mechanisms of photoprocesses in simple molecules and recombination accompanied by radiation. The book also offers information on general kinetics for gas-phase processes and basic theoretical frameworks for elementary processes. It features many useful problems, making it a valuable resource for students and researchers in molecular spectroscopy/molecular physics and chemical physics/physical chemistry. Preface 6 Acknowledgements 7 Contents 8 Abbreviations 11 Symbols 13 1 Introduction 19 2 General Kinetic Rules for Chemical Reactions, Collisional, and Intramolecular Processes 22 Abstract 22 2.1 Rates of Reaction, Collisional, and Spontaneous Processes. Rate Constants. Kinetic Types of Simple Processes 22 2.1.1 Kinetic Types of Simple Processes 28 2.2 Chemical Equilibrium. Equilibrium Constant 30 2.3 Arrhenius Equation 41 2.4 Complex Reactions. Consecutive Reactions. Steady-State Method 45 2.4.1 Steady-State Method 47 References 53 3 Theory of Elementary Processes 54 Abstract 54 3.1 Cross-Sections, Rate Constants, and Probabilities of Elementary Processes. The Detailed Balance Principle 54 3.2 Adiabatic Approximations. Potential Energy Curves and Surfaces 60 3.3 Intermolecular Interactions. Types of Intermolecular Interactions 66 3.3.1 Exchange Interaction 67 3.3.2 Direct Electrostatic Interactions 68 3.3.3 Polarization Interactions 70 3.3.4 Resonance Interactions 73 3.4 Semiempirical Model Potentials for Intermolecular Interactions 74 3.5 Descriptions of Collisional Processes Using Potential Energy Curves and Surfaces. Intramolecular Vibrational Relaxation in Polyatomic Molecules 76 3.6 Nonadiabatic Transitions. Perturbation Theory. Probabilities of Adiabatic and Nonadiabatic Transitions 87 References 94 4 Photolysis of Free Molecules 96 Abstract 96 4.1 Primary and Secondary Processes of Gas-Phase Photolysis. Quantum Yields 96 4.2 Radiative Electronic Transitions. Selection Rules for Radiative Electronic Transitions. Spin–Orbit Coupling and Spin-Forbidden Radiative Electronic Transitions 103 4.2.1 Allowed Radiative Electronic Transitions 103 4.2.1.1 General Selection Rules for Electric Dipole Transitions 103 4.2.1.2 Spin Selection Rules 104 4.2.2 Forbidden Electronic Transitions 105 4.2.2.1 Transitions in Polyatomic Molecules Allowed Due to Vibronic Interactions 105 4.2.2.2 Transitions in Polyatomic Molecules Allowed Due to Electronic-Rotational Interactions 106 4.2.2.3 Magnetic-Dipole and Electric-Quadrupole Transitions 106 4.2.3 Spin–Orbit Coupling and Spin-Forbidden Transitions 106 4.3 Absorption. Absorption Band Intensities. Einstein Absorption and Stimulated Emission Coefficients. Beer-Lambert Law. Oscillator Strength 113 4.4 Luminescence. Radiative Lifetime. Einstein Spontaneous Emission Coefficient 118 4.5 Franck–Condon Principle for Bound–Bound and Bound-Free Transitions 120 4.6 Intramolecular Perturbations. Selection Rules and Franck–Condon Principle for Intramolecular Perturbation. Perturbations Between Bound States 122 4.6.1 Perturbations Between Bound States of Diatomic Molecules 124 4.6.1.1 Perturbations Between States of the Same Symmetry 128 4.6.1.2 Perturbations Between Electronic States of Different Symmetry 130 4.6.1.3 Matrix Elements for Different Types of Perturbation 131 4.6.1.4 Hyperfine Interaction 135 4.6.1.5 Two-State Perturbation Model 137 4.6.1.6 Hyperfine Interactions Between Iodine Molecule Valence States 139 4.6.1.7 Hyperfine Interactions Between Iodine Molecule Ion-Pair States 141 4.6.2 Perturbations Between Bound States of Polyatomic Molecules. Anomalously Long Radiative Lifetime of Polyatomic Molecules 146 4.6.2.1 Vibronic Perturbations 147 4.6.2.2 Anomalously Long Radiative Lifetime of Polyatomic Molecules 147 4.7 Electronic Predissociation of Di- and Polyatomic Molecules. Types of Predissociation Processes 151 4.7.1 Predissociation of Diatomic Molecules 153 4.7.2 Predissociation of Polyatomic Molecules 157 4.8 Dissociation of Polyatomic Molecules. Long-Lived States of Polyatomic Molecules 158 References 165 5 Energy Transfer in Collisions 170 Abstract 170 5.1 Translational-Translational Energy Transfer (T ↔ T Exchange) 170 5.2 Rotational-Translational Energy Transfer (R ↔ T Exchange) 172 5.3 Vibrational Energy Transfer 174 5.3.1 V ↔ T, V ↔ R, T Processes 174 5.3.2 V-V Exchange 178 5.3.3 V-R Exchange 180 5.3.4 V-T Processes at High Vibrational Levels 181 5.4 The Influence of Nonadiabatic Effects on the Vibrational Relaxation Rate 182 5.5 Collision-Induced Nonadiabatic Transitions 184 5.5.1 Perturbation-Facilitated Processes 186 5.5.2 Perturbation-Irrelevant Transitions 191 5.5.2.1 Collision-Induced Predissociation of the {{\bf I}}_{2} \left( {B{{\bf 0}}_{u}^{ {\,+\,} } } \right) State 191 5.5.2.2 The {\hbox{CN}}\left( {A^{2} {\Pi }\to ^{Rg} X^{2} {{{\varvec \Sigma}}}^{ {\,+\,} } } \right),{\hbox{N}}_{2}^{ {\,+\,} } \left( {A^{2}\Pi _{ {{\rm u}}} \to ^{Rg} X^{2} {\Sigma }_{g}^{ {\,+\,} } } \right) CINATs 192 5.5.3 Collision-Induced Non-Adiabatic Transitions Between Dihalogen Ion-Pair States 201 5.5.3.1 Non-Adiabatic Transitions Between Iodine Ion-Pair States Induced by Collisions with Different Partners 201 5.5.3.2 Non-Adiabatic Transitions Between Chlorine Ion-Pair States 203 5.5.4 Collision-Induced Predissociation 206 5.6 Vibrational Relaxation Via a Complex of Electronic States 207 5.7 Electronic Deactivation 208 References 212 6 Weakly-Bound Complexes and Clusters 215 Abstract 215 6.1 Definitions 215 6.2 Hydrogen- and Halogen-Bonded Complexes 217 6.3 Van der Waals Complexes 217 6.3.1 General 217 6.3.2 RgX2 vdW Complexes 220 6.3.2.1 The RgF2 vdW Complexes 220 6.3.2.2 The RgCl2 vdW Complexes 221 6.3.2.3 The RgBr2 vdW Complexes 226 6.3.2.4 The RgI2 vdW Complexes 230 6.3.3 The RgXY vdW Complexes 257 6.3.3.1 The RgICl vdW Complexes 258 6.3.4 Molecule-I2 vdW Complexes 262 6.3.4.1 H2I2 vdW Complexes 263 6.3.4.2 N2I2 vdW Complexes 263 6.4 Rare Gas-Halogen Molecule Clusters 267 6.4.1 {\varvec Rg}_{{\varvec x}}^{1} {\varvec Rg}_{{\varvec y}}^{2} {\varvec I}_{2} Clusters 267 6.4.2 Rg2Hal2 Clusters 270 6.4.2.1 The Ne2Br2 Clusters 270 6.4.2.2 The Rg2Cl2 Clusters 271 6.5 RgMe vdW Complexes 272 References 272 7 Chemiluminescence 281 Abstract 281 7.1 Types of Chemiluminescent Processes. Rate Constants. Definitions 281 7.2 The Basic Patterns of the Recombination Accompanied by Radiation 286 7.2.1 Inverse Dissociation, Inversion of Rotational or Vibrational Predissociation 286 7.2.1.1 Inverse Dissociation on Repulsive PECs 288 7.2.1.2 Inverse Dissociation on Bound PECs 289 7.2.2 Inverse Electronic Predissociation 290 7.2.3 Termolecular Recombination Accompanied by Radiation 293 References 298 Solutions of the Problems 300 Index 303