Picosecond spectroscopy applied to the study of chemical and biological reactions

Abstract A large number of techniques are available to directly observe chemical reactions at the molecular level. Each of these techniques has limitations in both the molecular detail that can be obtained and the time scale over which an observation can be made. The ideal method for studying a chemical reaction would permit observation of both the nuclear and electronic structure with a temporal resolution equal to the time associated with a molecular vibration, 10−13to 10−14 sec. Technology has made sufficient progress in the last decade to make possible direct measurements of a few molecular parameters with a resolution between 10−12 and 10−13sec, while a large amount of data can be obtained with a resolution on the order of 5 to 10 psec. The area of research dealing with the measurement of phenomena on this time scale is known as picosecond spectroscopy. As the title denotes, this field is concerned with rapidly probing the response of molecular systems to optical radiation. The constraint of making optical measurements is necessitated because both sources and detectors with such a fast response are available only for the IR, visible, and UV portion of the spectrum. The techniques needed to perform picosecond measurements have been both elegant and expensive. Section II deals entirely with this technology and presents both the capabilities and limitations of the methods used to generate and detect picosecond radiation. Section III will cover applications of picosecond spectroscopy to a variety of chemical problems such as vibrational relaxation, energy transfer, and unimolecular decay. Section IV is concerned with applications to biological systems.