Resonance Raman spectroscopy instrumentation

Raman spectroscopy has enjoyed a dramatic improvement during the last few years the interference by fluorescence of impurities is virtually eliminated. Up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. In spite of its potential abilities, Raman spectroscopy has until recently not been extensively used for real-life polymer/additive-related problem solving, but does hold promise. Resonance Raman spectroscopy exhibits very high selectivity. Further improvements in spectropho-tometric measurement detection limits are also closely related to advances in laser technology. Apart from Raman spectroscopy, areas in which the laser is proving indispensable include molecular and fluorescence spectroscopy. The major use of lasers in analytical atomic... 

With recent developments in analytical instrumentation these criteria are being increasingly fulfilled by physicochemical spectroscopic approaches, often referred to as whole-organism fingerprinting methods.910 Such methods involve the concurrent measurement of large numbers of spectral characters that together reflect the overall cell composition. Examples of the most popular methods used in the 20th century include pyrolysis mass spectrometry (PyMS),11,12 Fourier transform-infrared spectrometry (FT-IR), and UV resonance Raman spectroscopy.16,17 The PyMS technique... 

The application of Raman and resonance Raman spectroscopy has been greatly influenced by instrumentation developments. Commercial... 

The high costs associated with specialist ultrafast laser techniques can make their purchase prohibitive to many university research laboratories. However, centralised national and international research infrastructures hosting a variety of large scale sophisticated laser facilities are available to researchers. In Europe access to these facilities is currently obtained either via successful application to Laser Lab Europe (a European Union Research Initiative) [35] or directly to the research facility. Calls for proposals are launched at least annually and instrument time is allocated to the research on the basis of peer-reviewed evaluation of the proposal. Each facility hosts a variety of exotic techniques, enabling photoactive systems to be probed across a variety of timescales in different dimensions. For example, the STFC Central Laser Facility at the Rutherford Appleton Laboratory (UK) is home to optical tweezers, femtosecond pump-probe spectroscopy, time-resolved stimulated and resonance Raman spectroscopy, time-resolved linear and non-linear infrared transient spectroscopy, to name just a few techniques [36]. 

Since its discovery in 1928, Raman spectroscopy has evolved in terms of the fundamental understanding of the process, instrumentation and applications. More advanced techniques such as Resonant Raman Spectroscopy (RRS) " ... 

The conditions which determine whether flash photolysis can be used to smdy a given chemical system are (i) a precursor of the species of kinetic interest has to absorb light (normally from a pulsed laser) (ii) this species is produced on a timescale that is short relative to its lifetime in the system. Current technical developments make it easy to study timescales of nanoseconds for production and analysis of species, and the use of instrumentation with time resolution of picoseconds is already fairly common. In certain specific cases, as we will see in the last part of this chapter, it is possible to study processes on timescales greater than a few femtoseconds. Once the species of interest has been produced, it is necessary to use an appropriate rapid detection method. The most common technique involves transient optical absorption spectroscopy. In addition, luminescence has been frequently used to detect transients, and other methods such as time-resolved resonance Raman spectroscopy and electrical conductivity have provided valuable information in certain cases. 

In addition to ordinary inelastic Raman scattering, two additional resonance enhancement forms of Raman spectroscopy have proven useful for the study of polymers UV resonance Raman spectroscopy and surface-enhanced Raman spectroscopy. These two resonance techniques use conventional instrumentation but exhibit useful enhancement effects. 

Since there are a large number of different experimental laser and detection systems that can be used for time-resolved resonance Raman experiments, we shall only focus our attention here on two common types of methods that are typically used to investigate chemical reactions. We shall first describe typical nanosecond TR spectroscopy instrumentation that can obtain spectra of intermediates from several nanoseconds to millisecond time scales by employing electronic control of the pnmp and probe laser systems to vary the time-delay between the pnmp and probe pnlses. We then describe typical ultrafast TR spectroscopy instrumentation that can be used to examine intermediates from the picosecond to several nanosecond time scales by controlling the optical path length difference between the pump and probe laser pulses. In some reaction systems, it is useful to utilize both types of laser systems to study the chemical reaction and intermediates of interest from the picosecond to the microsecond or millisecond time-scales. 

Control analyses rely on the use of appropriate procedures or measurements assuring the identity of the materials involved in each step of the manufacturing process from receipt of raw materials to delivery of the finished products. NIR spectroscopy is an advantageous alternative to wet chemical methods and instrumental techniques such as IR, Raman and nuclear magnetic resonance (NMR) spectroscopies for positive identification. 

Among the techniques ideally suited for in situ studies are infrared, Raman, and nuclear magnetic resonance (NMR) spectroscopies and extended x-ray absorption fine structure (EXAFS). While still relatively new, the scanning tunneling and atomic force microscopes are expected to play an increasingly important role in catalyst characterization. Both instruments permit visualization of a catalyst surface at the atomic level and hold the potential of showing how atoms and molecules interact with a surface. 

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