Solid Hydrogen: Theory of the Properties of Solid H2, HD, and D2

The solid molecular hydrogens are the simplest and most fundamental molecular solids. Except at ultrahigh pressures on the order of a few mega- bars, where a transition to a metallic, atomic phase is expected, these solids are true molecular crystals in which the molecules retain their identity with properties not too different from those of the free molecules. At energies below the electronic excitation energy, the thermal and spectroscopic pro- perties of these solids are determined by the translational, rotational, and intramolecular vibrational motions of the interacting molecules. The theo- retical analysis of the solid-state properties in terms of the free molecules and the intermolecular interactions forms the main topic of this book. The available detailed knowledge of the properties of the free molecules makes it feasible to carry out this program to a large extent on the basis of first principles, and this is one of the attractive features of these systems. The solid hydrogens are dominated by quantum effects, the most out- standing property being that the rotation of the molecules is free down to the lowest temperatures, in the sense that the rotational quantum number J characterizing the rotational motion of the free molecules remains a good quantum number in all of the solid-state phases except at ultrahigh pressures.

Table of Contents:
1. Properties of Isolated Hydrogen Molecules.- 1.1 The Adiabatic Approximation.- 1.2 The Rotation-Vibration States.- 1.3 The Molecular Multipole Moments and Polarizabilities.- 1.4 The Dunham Model.- 1.5 Nuclear Symmetry Species for Homonuclear Molecules.- References.- 2. The Intermolecular Interaction.- 2.1 Definition of the Intermolecular Interactions.- 2.2 The Long-Range Intermolecular Interactions.- 2.3 The Short-Range Intermolecular Interactions.- 2.4 Models for the Pair Potential.- References.- 3. Pure Vibrational Excitations.- 3.1 The fcc and hcp Structures.- 3.2 Single-Molecule Perturbations.- 3.3 Vibrational Energy Bands.- 3.4 Localized Vibrational States.- 3.5 The Vibrational Raman Spectrum.- References.- 4. Rotational Excitations in J = 0 Solids.- 4.1 Crystal-Field Interactions.- 4.2 Pure Rotational Excitations.- 4.3 Mixed Rotation-Vibration Excitations.- 4.4 Rotation Raman and Infrared Spectra.- References.- 5. Lattice Vibrations and Elastic Properties.- 5.1 Lattice Vibrations in the Harmonic Approximation.- 5.2 Lattice Vibrations in Quantum Crystals.- 5.3 Elastic Properties and the Anisotropic Debye Model for the hcp Lattice.- 5.4 Two-Particle Distribution Functions and Correlation Matrices.- References.- 6. Single J = 1 Impurities in J = 0 Solids.- 6.1 Crystal-Field Interactions in a Rigid Lattice.- 6.2 Effect of Static Phonon Renormalization.- 6.3 Dynamic Crystal-Field Effects.- 6.4 Specific Heat and NMR Properties.- References.- 7. Clusters of J = 1 Impurities in J = 0 Solids.- 7.1 Models for Cluster Distributions.- 7.2 Properties of Isolated Clusters.- 7.3 Spectroscopy of nn Pairs of J = 1 Molecules.- 7.4 Finer Details of the nn Pair Interaction.- 7.5 Interactions between More Distant Neighbors.- References.- 8. The Ordered Phases.- 8.1 Orientational andStructural Phase Changes.- 8.2 The Four-Sublattice Structure of Pure J = 1 Solids.- 8.3 The Order-Disorder Transition in the fcc Solids.- 8.4 Librons in Pure J = 1 Solids.- 8.5 J = 0 Impurities in J = 1 Solids.- 8.6 Ordering in J = 0 Solids at Ultrahigh Pressures.- References.- 9. Rotation Diffusion and Ortho-Para Conversion.- 9.1 Ortho-Para Conversion Processes.- 9.2 Rotation Diffusion at Small J = 1 Concentrations.- 9.3 Rotation Diffusion at Small J = 0 Concentrations.- 9.4 Experimental Results on Rotation Diffusion.- References.- Appendix A. Spherical Tensor Formalism.- Appendix B. Lattice Sums.