Theory.- 1. The Symmetry Groups and Rotation-Vibration Energy Levels of Some Very Nonrigid Molecules.- 2. Vibration-Inversion-Torsion-Rotation Energy Levels and Vibrational Resonances in the Methylamine Molecules.- 3. The Excited State Dynamics of Conjugated Molecules: Theoretical Studies of Slow Vibrations.- Vibrational Spectroscopy.- 4. Vibrational Potential Energy Surfaces of Non-Rigid Molecules in Ground and Excited Electronic States.- 5. Structural Information on Large Amplitude Motions.- 6. Conformational Stability of Five-Membered Ring Molecules.- 7. The Structure and Dynamics of Van Der Waals Molecules.- 8. Applications of Asymmetric Top Contour Simulation to Conformational Equilibria.- Microwave Spectroscopy.- 9. Large Amplitude Motions in Two Ring Molecules.- 10. Rotational Studies of Four-and Five-Membered Ring Molecules.- 11. Large Amplitude Motions in Molecular Complexes.- 12. Accurate Structures of Non-Rigid Molecules by Microwave Spectroscopy.- 13. Tunneling Motions in Sulfur Dioxide Complexes.- 14. Recent Gas-Phase Studies of Intermolecular Hydrogen Bonding.- 15. Millimeter- and Submillimeter-Wave Spectroscopy of Non-Rigid Transient Molecules: Analysis of Silane and Acetylene Plasmas.- Ab Initio Calculations.- 16. The Cis Monobridged Equilibrium Geometries of Si2H2, Ge2H2, Al2H2, and Ga2H2: A Fundamentally New Type of Molecular Structure.- 17. Ab Initio Anharmonic Vibrational Analyses of Non-Rigid Molecules.- 18. The Use of Natural Coordinates in Molecular Geometry Optimizations.- 19. Ab Initio Molecular Orbital Calculations of the Infrared Spectra of Interacting Water Molecules. Complexes of Water With Carbon Dioxide and Nitrous Oxide..- 20. Large Amplitude Motion In Oxalyl Chloride.- Electron Diffraction.- 21. Gas-Phase electron Diffraction Applied to Molecules Undergoing Large-Amplitude Motion.- 22. Conformational Analysis By Gas Electron Diffraction.- 23. Linear, Bent, and Quasilinear Molecules.- 24. Structures and Conformational Analysis of Monosubstituted Cyclopropanes of the Type: c-Pr-XY and c-Pr-CH -XY (X = Si, Ge; Y = H, F, Cl).- 25. Small Forces and Large Molecular Distortions.- 26. Gas-Phase Structures and Conformational Properties of Malonic Acid Derivatives, {CY2(COX)2}, as Studied By Electron Diffraction and ab Initio Calculations.- Electronic Excited States, Fluorescence Spectra, and Dynamics.- 27. Molecular Conformations in Electronic Excited States.- 28. A Comparison of the Methyl Torsion and Aldehyde Wagging Dynamics in the Ground and First Excited States of Acetaldehyde and Thioacetaldehyde.- 29. Isolation and Assignment of Organic Molecular Conformers via Laser Induced Fluorescence Spectroscopy of Jet-Cooled Molecular Beams.- 30. The Structure and Dynamics of Van Der Waals Clusters as Studied by Formation of Negative Cluster Io