The lattice dynamics of molecular crystals has undergone an enor mous progress in these last twenty years or so. The experimental and theoretical advances have been realized by two different approaches. From one side molecular spectroscopists have been primarily interested in the vibrational properties of the molecules themselves subjected to the perturbing influence of the crystal environment. From the other side the lattice dynamical theory familiar in solid state physics for atomic lattices has been extended to molecular arrays. Although the overlap between the two approaches has been considerable the reference material is rather scattered in specialized papers. The purpose of this book is to partly fill this gap and to discuss the lattice dynamical theory of molecular crystals in a compact and specialized form. As such, the book is not intended exclusively for researchers and specialists in the field but also for graduate students entering an activity in solid state mo lecular spectroscopy.

1 Lattice Dynamics

1.1 Introduction
1.2 The Dynamical Equations in Cartesian Coordinates
1.3 Dispersion Curves. Acoustic and Optical Modes
1.4 Invariance Conditions
1.5 Molecular Coordinates
1.6 The Dynamical Equations in Molecular Coordinates
2 Symmetry
2.1 Space Group Symmetry
2.2 Irreducible Representations of the Translational Group
2.3 Irreducible Representations of the Space Groups
2.4 Time Reversal
2.5 Symmetry of the Dynamical Matrix
2.6 Symmetry Properties of Vibrational States
2.7 Selection Rules
3 Intermolecular Potentials
3.1 The Crystal Potential
3.2 The Intramolecular Potential
3.3 The Intermolecular Potential
3.4 Intermolecular Force Constants
3.5 Lattice Sums and Ewald's Method
2.6 Calculation of Phonon Frequencies
4 Anharmonic Interactions
4.1 Introduction
4.2 The Crystal Hamiltonian
4.3 Quantum Field Treatment of Phonons
4.4 The Hamiltonian Renormalization Procedure
4.5 The Self-Consistent Phonon Method
4.6 The Method of the Green's Functions
4.7 Thermal Strain
4.8 Anharmonic Calculations
5 Two-Phonon Spectra of Molecular Crystals
5.1 Introduction
5.2 General Considerations
5.3 Two-phonon Density of States
5.4 Two-phonon Absorption Coefficients
6 Infrared and Raman Intensities in Molecular Crystals
6.1 Introduction
6.2 Historical Survey
6.3 Electrostatic Model of Infrared and Raman Intensities of Molecular Crystals.