Inert Gases

Research involving the chemical physics of the inert or rare gases continues unabated. This small volume is meant to deal with advances that have occurred in three selected areas over the past decade. It forms a natural outgrowth of earlier reviews and volumes that have dealt almost exclusively with pure rare-gas solids. Originally, a single chapter was envisaged to cover the topic of alloys and impurities in solid rare gases. However, over the past ten years this single chapter spawned many offshoots and eventually the project became too large for a single volume. Thus the present book contains only a small subset of possbile topics involving rare-gas solids intentionally doped with impurities. Chapter 1 gives a brief overview of current research devoted to the rare gases. This is followed by a comprehensive, self-contained chapter dealing with the most recent developments in the area of interatomic inter­ actions. Chapter 3 is concerned with the lattice dynamics of rare-gas solids doped with an impurity which is either another rare-gas or a small molecule. The final chapter deals with the spectroscopy of vibrating and rotating di­ atomic impurities in rare-gas solids. The birth of this volume was not without its labour pains. I should like to take this opportunity to thank the various people who have at one time or another been involved throughout its gestation period. Clearly, many important topics are omitted from this volume.

1. Argon and Its Companions..- 1.1 Prologue: Inert, Rare or Noble?.- 1.2 Research with Inert Gases.- 1.3 Outline of the Present Book.- References.- 2. Interatomic Potentials for Rare-Gases: Pure and Mixed Interactions.- 2.1 Background.- 2.2 What Probes What?.- 2.2.1 Bulk Properties.- 2.2.2 Molecular-Beam Experiments.- 2.2.3 Spectroscopic Data.- 2.3 Review of Recent Research on Pure Interactions.- 2.3.1 Helium.- 2.3.2 Neon.- 2.3.3 Argon.- 2.3.4 Krypton.- 2.3.5 Xenon.- 2.4 Review of Recent Research on Unlike Interactions.- 2.4.1 Helium-Rare-Gas Systems (He-Ne, He-Ar, He-Kr and He-Xe).- 2.4.2 Neon-Rare-Gas Systems (Ne-Ar, Ne-Kr, Ne-Xe).- 2.4.3 Argon-Krypton, Argon-Xenon, Krypton-Xenon.- 2.5 Combining Rules.- 2.5.1 Berthelot-Lorentz Rules.- 2.5.2 Kohler Rules.- 2.5.3 Hudson-McCoubrey Rules.- 2.5.4 Fender-Halsey Rules.- 2.5.5 Sikora Rules.- 2.5.6 Hiza-Duncan Rules.- 2.5.7 Total Cross-Section Rules.- 2.6 Conclusions.- Appendix: 2.A Interatomic Potential Functions.- 2.B Interatomic Potential Parameters.- 2.C Predictions of Collisons Cross-Sections by Potentials.- References.- 3. Dynamics of Impure Rare-Gas Crystals.- 3.1 Background.- 3.2 Lattice Dynamics of Impure Crystals.- 3.2.1 Historical Review.- 3.2.2 Pure Crystals.- 3.2.3 An Isolated Impurity.- 3.2.4 Central Force-Constant Model.- 3.2.5 Far-Infrared Absorption.- 3.2.6 Mossbauer Effect.- 3.2.7 Heat Capacity.- 3.2.8 Neutron Scattering.- 3.3 Theoretical Studies.- 3.3.1 Application of the CFC Model.- a) Potentials.- b) Relaxation Effects.- c) Three-Body Forces.- d) Phonon Density of States.- 3.3.2 Computer Simulation.- 3.4 Experimental Studies.- 3.4.1 Rare Gases in RGS.- a) Argon Doped with Krypton.- b) Argon Doped with Neon.- c) Argon Doped with Helium.- d) Argon Doped with Xenon.- e) Krypton Doped with Argon.- f) Krypton Doped with Xenon.- 3.4.2 Molecules in RGS.- a) Homonuclear Diatomics.- b) Heteronuclear Diatomics.- c) RGS Doped with Methane.- 3.4.3 Matrix-Isolated Species.- a) Molecular Ions.- b) Molecules.- c) Atoms.- 3.5 Summary.- References.- 4. Spectroscopy of Vibrational and Rotational Levels of Diatomic Molecules in Rare-Gas Crystals.- 4.1 Background.- 4.2 Experimental Techniques and Results.- 4.2.1 Experimental Techniques.- a) Sample Preparation.- b) Spectroscopy (Conventional Versus Laser).- c) Saturation Spectroscopy or Hole Burning.- d) Time-Resolved Spectroscopy.- 4.2.2 Spectroscopic Studies of Ground Electronic State Molecules.- a) Vibrational Transitions.- b) Rotational Transitions.- c) Phonon Sidebands.- 4.2.3 Time-Resolved Experiments.- a) Infrared Spectroscopy.- b) Visible Spectroscopy.- 4.3 Intermolecular Interaction in Rare-Gas Crystals Containing Molecular Defects.- 4.3.1 Intermolecular Potential Between a Rare-Gas Atom and a Diatomic Molecule.- a) Atom-Atom Potential.- b) Multiparameter Potential Functions.- c) Ab Initio Potential Surfaces.- d) Charge Transfer and Hydrogen Bonding.- 4.3.2 The Interaction Hamiltonian.- a) Energy Levels.- b) Relaxation Processes.- 4.4 Perturbation of Energy Levels.- 4.4.1 Influence of a Diatomic Impurity on Lattice Energies.- a) Effect of Isotropic Terms.- b) Effect of Internal Molecular Motions.- c) Description of Lattice Vibrations Through Molecular Dynamics.- d) Phonon Sidebands in IR Spectra of the Guest Molecule.- 4.4.2 Perturbation of the Molecular Energy Levels.- a) Vibrational Matrix Shift.- b) Rotational Matrix Shift.- 4.5 Population Relaxation Processes.- 4.5.1 Radiative Relaxation.- 4.5.2 Vibrational Relaxation to Phonons.- 4.5.3 Vibration to Rotation Energy Transfer.- 4.5.4 Vibrational Energy Transfer.- a) Microscopic Processes Among Molecules in Rare-Gas Crystals.- b) Microscopic Probabilities for Vibrational Energy Transfer.- c) Macroscopic Kinetics for Vibrational Energy Transfer.- d) Comparison Between Theory and Experiment.- 4.5.5 Radiationless Rotational Relaxation.- a) The Direct Process.- b) Raman and Orbach Processes.- 4.6 Spectral Line Shapes and Dephasing Processes.- 4.6.1 Homogeneous Broadening: T1 and T2 Relaxation Processes.- 4.6.2 Vibrational Dephasing in Matrix-Isolated Molecules.- 4.6.3 Line Shape Function and Dephasing.- a) Isolated Vibrational Levels with a Large Spacing.- b) Additional Low-Energy Levels in the Molecule.- 4.6.4 Comparison Between Theory and Experiment.- 4.7 Concluding Remarks.- References.- Additional References with Titles.