Single nonlinear Raman techniques

The Application oi Single-Pulse Nonlinear Raman Techniques to a Liquid Photolytic Reaction... 

Such single-mode lasers, often pulse amplified by dye laser amplifiers pumped by injection-locked Nd YAG lasers, are used in nonlinear Raman techniques by which an instrumental resolution better than 0.001 cm is achieved (Esherick and Owyoung (1982), Schrotter et al. (1988a)). 

This chapter describes the application of these techniques to a liquid photolytic reaction. The motivation was the assessment of the capabilities and limitations of single-pulse nonlinear Raman spectroscopy as a probe of fast reactions in energetic materials. 

Thus far, we have examined vibrational spectroscopy using IR absorption spectroscopy, what we called in Ch. 3 one photon method , a general type that encompasses most experiments in spectroscopy. There exist, however, other types of spectroscopy to observe vibrations. These are for instance Raman spectroscopy, which is also of a current use in chemical physics and may be considered a routine method. Other less known methods are modem time-resolved IR spectroscopies. All these methods are two-photon or multiphoton spectroscopies. They do not involve a single photon, as in absorption, but the simultaneous absorption and emission of two photons, as in Raman and in other scattering experiments, or the successive absorption(s) and emission(s) of photons that are coherently delayed in time, as in time-resolved nonlinear spectroscopies. By coherently , we assume the optical waves that carry these two photons keep a well-defined phase difference. In this latter type of spectroscopy, we include all modem set-ups that involve time-controlled laser spectroscopic techniques. We briefly sketch the interest of these various methods for the study of H-bonds in the following subsections. 

IR and Raman spectroscopy are both quantitative techniques, in that both the IR absorbance and the Raman scattered intensity are, to a first approximation, linearly proportional to the number density of vibrating species. Although quantitative information can be extracted from a single absorbance or scattered intensity (after calibration against absolute standards), it is more usual to measure the ratio of the analyte band of interest against an independent internal standard, in order to allow for variations in pathlength, deviations from ideality, detector nonlinearity, etc. The reader is referred elsewhere for a full discussion of quantitative methods (including multivariate techniques) [9, 10]. 

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