Lasers and Chemical Change

Lasers and chemical change is the study of radiation and molecules in dis­ equilibrium. The distinguishing feature of such systems is the extreme de­ parture from thermal equilibrium: the radiation is usually confined to a narrow frequency range, is well coll imated, and is far brighter than black body radiation; the chemical composition and also the distribution of mole­ cules over their different energy states are often markedly displaced from that expected at equilibrium. Such systems can be used as a source of laser radiation and, reversedly, lasers can rapidly and selectively displace mole­ cular systems from equilibrium. The subsequent evolution of the initially prepared state can then be monitored - again using lasers. One purpose of this book is to introduce the concepts required to d- cuss systems of radiation and molecules in disequilibrium. These include the physics of (laser) radiation and of radiation-matter interaction and molecular structure and spectroscopy. Excellent textbooks of these topics are available and our survey (in Chap. 3) is only intended to accent the es­ sential points, with special reference to atomic and molecular radiation physics. Considerably more attention is given to the topic of disequilibrium in chemical systems (Chap. 2). In particular we consider both inter- and intra­ molecular dynamics with special reference to energy requirements and energy disposal in chemical reactions and to what goes on in between - intramole­ cular energy migration.

1. Lasers and Chemical Change.- 1.1 Light Amplification and Population Inversion in Chemical Processes.- 1.2 Molecular Rate Processes.- 1.3 Photoselective Chemistry.- 1.3.1 The Di screte Spectrum.- 1.3.2 The Quasicontinuum.- 1.3.3 Radiationless Transitions.- 1.3.4 Dissociative Continuum.- 1.3.5 Ionization.- 1.4 The Road Ahead.- 2. Disequilibrium.- 2.1 Specificity and Selectivity of Chemical Reactions.- 2.1.1 Overview: Microscopic Disequilibrium.- 2.1.2 The Detailed Rate Constant.- 2.1.3 Detailed Balance.- 2.1.4 Energy Disposal and Energy Consumption.- 2.1.5 The Reaction Probability Matrix.- 2.1.6 Measures of Specificity and Selectivity.- 2.1.7 The Maximum Entropy Formalism.- 2.2 Surprisal Analysis.- 2.2.1 The Prior Distribution.- 2.2.2 The Surprisal.- 2.2.3 Vibrational Surprisal.- 2.2.4 The Rotational State Distribution.- 2.2.5 Electronic Excitation.- 2.2.6 Polyatomic Molecules.- 2.2.7 Surprisal Analysis and Collision Dynamics.- 2.2.8 On the Role of Reagent Translation.- 2.3 Molecular Reaction Dynamics.- 2.3.1 Computational Studies.- 2.3.2 Potential Energy Surface(s).- 2.3.3 Bond-Tightening Models.- 2.3.4 Kinematic Models of Collision Dynamics.- 2.3.5 Unimolecular Processes — The RRK Approach.- 2.3.6 Unimolecular Processes — Selectivity and Specificity.- 2.3.7 Preparing the Initial State.- 2.4 State-to-State Processes.- 2.4.1 The Prior Detailed Rate Constant.- 2.4.2 The Exponential Gap Representation.- 2.4.3 Reactive Collisions.- 2.4.4 The Adiabaticity Parameter.- 2.4.5 Polyatomic Molecules.- 2.4.6 Temperature Dependence.- 2.4.7 Electronic Energy Transfer.- 2.4.8 A Laser Bridge for the Exponential Gap.- 2.4.9 Intramolecular Electronic to Vibrational Energy Tansfer: Radiationless Transitions.- 2.5 Macroscopic Disequilibrium.- 2.5.1 The Master Equation: Relaxation of Harmonic Oscillators.- 2.5.2 Rotational Relaxation.- 2.5.3 Separation of Time Scales.- 2.5.4 Vibrational Anharmonicity and V-V Up-Pumping.- 2.5.5 Intermode V-V Transfer.- 2.5.6 From Macroscopic Relaxation to Microscopic Information.- 2.5.7 Thermodynamics of Molecular Disequilibrium.- 2.5.8 Laser Thermodynamics.- Appendices.- 2.A. The Prior Distribution.- 2.B. Practical Surprisal Analysis.- 2.C. Statistical Models, Prior Distributions, and Collision Dynamics.- 2.D. Derivation of the Treanor Distribution.- 3. Photons, Molecules, and Lasers.- 3.1 Interaction of Molecules with Radiation.- 3.1.1 The Golden Rule.- 3.1.2 The Line Shape Function.- 3.1.3 Coherent Interaction.- 3.2 Essential Physics of Lasers.- 3.2.1 The Gain Coefficient.- 3.2.2 Laser Oscillators.- 3.2.3 Laser Radiation and Modes.- 3.2.4 The Laser Rate Equations.- 3.3 Survey of Atomic and Molecular Spectroscopy.- 3.3.1 Atomic Spectra.- 3.3.2 Molecular Spectra.- 3.3.3 Electronic Spectra of Diatomic Molecules.- 3.3.4 Infrared Spectra of Diatomic Molecules.- 3.3.5 Energy Levels of Polyatomic Molecules.- 3.3.6 Infrared Spectra of Polyatomic Molecules.- 3.3.7 The Near Ultraviolet Spectrum of Carbonyl Compounds.- 3.4 Laser Sources.- 3.4.1 Laser Specifications.- 3.4.2 Exciplex Lasers.- 3.4.3 Dye Lasers.- 3.4.4 C02 Lasers.- 4. Chemical Lasers.- 4.1 Survey of Chemical Lasers.- 4.2 Lasing Conditions in Chemical Lasers.- 4.3 Operati on.- 4.3.1 Flash Photolysis: The Iodine Laser as a Model Case.- 4.3.2 Hydrogen Halide Chemical Lasers.- 4.3.3 The Chemical CO Laser.- 4.4 Chemical Laser Kinetics.- 4.4.1 The Rate Equations.- 4.4.2 Rotational Equilibrium.- 4.4.3 Rotational Nonequilibrium.- 4.4.4 cw Chemical Lasers.- 4.5 Some Applications of Chemical Lasers.- 4.5.1 Total Rate Constants, Kinetic Isotope Effects.- 4.5.2 Vibrational Population Ratios from Threshold Time Measurements.- 4.5.3 Gain Probing.- 4.5.4 Energy Transfer Measurements: An Example.- 4.5.5 An Industrial Diagnostic Application.- 5. Laser Chemistry.- 5.1 The Laser Evolution.- 5.2 Bimolecular Reactions.- 5.2.1 Molecular Beam Studies.- 5.2.2 Reactions in the Bulk.- 5.3 Electronic Excitation of Polyatomic Molecules.- 5.3.1 Direct Photodissociation: The A State of ICN.- 5.3.2 Photopredissociation: Formaldehyde.- 5.3.3 Excitation of Bound Electronic States: Biacetyl and Glyoxal.- 5.4 Multiphoton Activation and Fragmentation.- 5.4.1 The Nature of Multiphoton Excitation.- 5.4.2 The Rate Equation Approach.- 5.4.3 Nondissociative Reactions Induced by Multiphoton Absorption.- 5.4.4 Multiphoton Ionization (MPI).- 5.5 The “Compleat” Laser Chemist.- 5.5.1 Prepari ng the Sample.- 5.5.2 Excitation and Probing Techniques.- 5.5.3 Laser-Oriented Absorption Measurements.- 5.6 From the Laboratory to Large-Scale Laser Chemistry.- 5.6.1 Practical Photoselective Chemistry.- 5.6.2 State Selective Chemistry.- 5.7 Synergism.- References.- Author Index.