Applications of Picosecond Spectroscopy to Chemistry

With the development of lasers that can generate light 11 14 pulses ranging from 10- - 10- sec duration, and capable of 13 peak powers in excess of 10 watts scientists have been able to investigate the interactions of light with matter in a time and power domain not previously possible. These ultrashort laser pulses provide a powerful tool for the study of chemical phenomena at the most fundamental level. Many of the elementary processes of importance in chemistry including energy dissipa­ tion, molecular motions, structural and chemical changes occur on a very short time scale and thus require special approaches. Th~ use of ultrashort laser pulses to perturb and to probe systems of interest affords a direct approach to the time reso­ lution of very rapid chemical phenomena. It was recognition of the impact of these relatively new approaches to chemical phenomena that motivated NATO to sponsor a meeting on the applications of picosecond spectroscopy in chemistry. The primary aim of the NATO workshop was to gain some perspective on the status of the field in terms of present research activities, technological developments and if possible the difficult task of sensing future directions. The way we decided to approach these issues was to gather together the main contributors to the field, fortunately many of whom were able to attend, to present their work and to participate in what turned out to be lively discussions of the field.

Inhalt

I Photochemistry.- The Sub-Nanosecond Regime in Photosynthesis.- Picosecond Laser Photolysis Studies of Photo-Induced Charge Transfer and Related Phenomena.- Application of Picosecond Spectroscopy to Organic Reaction Mechanisms.- Studies of the Chemical Intermediate Diphenyl-Carbene: Intersystem Crossing, Solvent Effects on Dynamics, Spin State Selective Chemistry, Photochemistry of the Excited Triplet State.- II Energy Relaxation and Molecular Motions in Condensed Media.- Photochemical Isomerization Viewed as a Model for Activated Barrier Crossing in Solution.- Dynamics of the Radiationless Relaxations in Triphenylmethane Molecules and the Influence of Solvent-Solute Interactions.- Verification of Optical Redfield Theory in Doped Molecular Solids.- Picosecond Fluorescence Decay of Organic Chromophores and Biological Pigments, Monitored With a Synchroscan Streak Camera.- Non-Linear Optical Spectroscopy and Molecular Dynamics in Liquids.- III Vibrational Relaxation.- Picosecond Vibrational Dephasing Experiments in Liquids under High Laser Depletion Conditions.- Ultrafast Coherent Infrared and Raman Spectroscopy of Gases and Liquids.- Picosecond Processes in Chemical Systems: Vibrational Relaxation.- Time Resolved Spectroscopy and Dynamics of Large Amplitude Vibrational Motion in Molecular Liquids And Crystals.- Fluorescence Studies of Very Short-Lived Excited States of Aromatic Molecules.- IV Isolated Molecules.- Single Vibrational Level Dependence of Picosecond Fluorescence in the Channel 3 Region of Benzene.- Picosecond Photo-Chemistry and Spectroscopy in Supersonic Beams.- Photodissociation of S-Tetrazine and Vibrational Predissociation Processes of its Argon Van Der Waals Complexes.- V Spectroscopic Techniques.- Spectroscopy with Femtosecond Optical Pulses.- Alternative Techniques for Picosecond Spectroscopy.- List of Participants.