These proceedings report the lectures and seminars presented at the NATO Advanced Study Institute on "The Spectroscopy of the Excited State," held at Erice, Italy, June 9-24, 1975. This Institute was an activity of the International School of Atomic and Molecular Spectroscopy of the "Ettore Majorana" Centre for Scientific Culture. The Institute consisted of a series of lectures on the spectroscopic properties of materials in excited electronic states, that, starting at a fundamental level, finally reached the current level of research. The sequence of lectures and the organization of the material taught were in keeping with a didac tical presentation. In essence the course had the two-fold pur pose of organizing what was known on the subject, and updating the knowledge in the field. The formal lectures were complemented by seminars whose abstracts are also included in these proceedings. The proceedings report also the contributions sent by Professors R.G.W. Norrish and S. C1aesson who, unfortunately, were not able to come because of illness. A total of 62 participants and 7 lecturers came from the following countries: Belgium, Canada, Czechoslovakia, France, Germany, Israel, Italy, Japan, Netherlands, Norway, Pakistan, Poland, Sweden, Switzerland, the United Kingdom, the United States and Venezuela. The secretaries of the course were: A. La Francesca for the administrative aspects of the meeting and P.Papagiannakopou10s for the scientific aspects of the meeting.

Inhalt
Interaction of Radiation with Atoms and Molecules.- Abstract.- I. Introduction.- II. Quantum Theory of Molecular Systems.- III. Quantum Theory of the Radiative Field.- IV. Interaction of a Radiative Field with a Charged Particle.- V. Absorption and Emission of Radiation.- References.- to Molecular Spectroscopy.- Abstract.- I. Historical Introduction.- II. Theory of Electronic Spectra.- III. Molecular Orbitals and Spectra of Triatomic Molecules.- References.- Laser Excitation of Optical Spectra.- Abstract.- I. Characteristics and Types of Lasers.- II. Excitation of Molecular Spectra.- III. Saturation Spectroscopy.- IV. Two-Photon Spectroscopy.- References.- Techniques of Flash Photolysis.- Abstract.- I. Introduction.- II. Discharge Circuits.- III. Examples of Flash Photolysis Apparatuses.- IV. Kinetic Studies by Means of Flash Photolysis.- V. Calculation of Rate Processes Which Are as Fast as the Flash Decay.- VI. Numerical Analysis of Experimental Data References.- Some Fast Reactions in Gases Studied by Flash Photolysis and Kinetic Spectroscopy.- I. Introduction.- II. Flash Photolysis and Kinetic Spectroscopy.- III. Vibrational Excitation by Primary Reaction. The Flash Photolysis of Nitrosyl Halides -- Vibrational Relaxation.- IV. Vibrational Excitation by Secondary Reactions.- V. Application of the Adiabatic Method. The Study of Explosive Processes Exemplified by the Oxidation of Hydrides.- VI. A General Mechanism for the Combustion of Hydrides.- References.- Electronic and Vibrational Energy Transfer.- Abstract.- I. Introduction.- II. Vibration Translation Transfer.- III. Vibration Vibration Transfer.- IV. Vibrational Relaxation in Excited Electronic States.- V. Electronic to Vibrational Energy Transfer.- VI. Electronic Electronic Transfer.- References.-The Chemical Production of Excited Species.- Abstract.- I. Introduction.- II. The Formation of Excited Species in Combination Processes.- III. Chemiluminescence in Atom Transfer Processes.- IV. Chemiluminescence in Other Chemical Systems.- References.- Two-Photon Spectroscopy in the Gas Phase.- Abstract.- I. Introduction.- II. Theory.- III. Methods of Assignment in Two-Photon Spectroscopy.- IV. Lifetimes.- References.- Lifetime Spectroscopy.- Abstract.- I. Introduction.- II. New Techniques.- III. Conclusion and Future.- References.- The Study of Electronic Spectra in Crystalline Solid Solutions.- Abstract.- I. Introduction.- II. Naphthalene in Durene.- III. Orientation of Molecules in Solid Solution.- IV. Spectrum Analysis.- V. Conclusions.- References.- Core Excitation and Electron Correlation in Crystals.- Abstract.- I. Fundamentals of Core-Exciton Theory.- II. Vacuum-Ultraviolet Absorption of Alkali Halides.- III. X-Ray Spectroscopy of Transition-Metal Compounds.- References.- Molecular Excitons in Small Aggregates.- Abstract.- I. Atomic and Molecular Excitons.- II. The Strong-Coupling Molecular Exciton: Dimers.- III. Phenomenology of Exciton States in Dimers.- IV. Linear Chain Polymers.- V. Exciton States of Helical Polymers.- VI. Exciton States in Molecular Lamellar Arrays.- VII. Molecular Exciton in Spherical Arrays.- VIII. Dynamical Aspects and Photosensitization.- References.- Singlet Molecular Oxygen: From a Scientific Curiosity to a Ubiquitous Chemical Species.- Triplet State Excitation Phenomena.- Spectroscopic Theory of the Solvent Cage.- Multiple Excitation in Composite Molecules.- Long Seminars (Abstracts).- Optical Spectroscopy of Molecular Ions.- Some Properties of the Excited States of Molecular Crystals.- Time-Resolved Spectroscopy of Self-Trapped Excitons in Alkali-Halide Crystals.- Molecular Aspects of Photochemical Dissociations.- Energy Migration in Solids.- Photoionization Resonance Spectra.- Electron Spectroscopy.- Short Seminars (Abstracts).- The 22P State of the Li Atom.- The Generator Coordinate Method and Molecular Vibrations.- Magnetic Dichroism Spectroscopy.- The Chemiluminescing Products of the Disilane-Fluorine, Disilane-Chlorine and Disilane-Ozone Reactions.- Collisional Transfer of Excitation in High-Pressure Rare Gases and Mixtures.- A Shock Tube-Laser Schlieren Measurements of the Dissociation of Molecular Chlorine.- Core Excitons in Synchrotron Radiation Absorption Spectra.- Reactions of Singlet Excited Dyes in Sensitized Photo-Oxidations.- A Model System for Photobiology: The Azoaldolase.- Relaxed Excited State of F-Centers.- List of Contributors.