Resonance Raman Instrumentation

Resonance Raman spectroscopy combines both vibrational and electronic spectroscopies. The vibrational spectrum at a particular excitation wavelength provides the first dimension. The excitation spectrum, the intensity of each vibrational band as a function of the excitation wavelength, provides the second dimension. Since most molecules have resonance enhancement in the UV, this approach is quite general, but not universal. The availability of a range of excitation frequencies from the laser source makes exploitation of this form of Raman scattering possible. 

Detection of UVRR spectra is con tlicated by a number of experimental difficulties the photooxidation and photodestruction of molecules, distortion of spectral information due to optical saturation phenomena and photoinduced transients, and fluctuations of the scattered light intensity in inhomogeneous samples. 

---

The basic elements of a SERS experimental setup are identical to those used in a normal Raman or resonance Raman instrument. A line diagram of such a Raman spectrometer follows ... 

Typical Instrumentation and Methods for Doing Time-Resolved Resonance Raman (TR ) Experiments... 

TYPICAL INSTRUMENTATION AND METHODS FOR DOING TIME-RESOLVED RESONANCE RAMAN (TR ) EXPERIMENTS... 

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. 

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... 

Experimentally, several precautions must be taken if reliable Raman data are to be obtained from solution studies. Firstly, the instrumental slit-width should be appreciably smaller than the half-width of the band to be studied. This means that slits wider than 2 cm-1 are to be avoided. Secondly, photolytic decomposition of the sample and local boiling of the solvent have also to be avoided. Careful choice of laser frequencies, use of a low incident power and, if necessary, sample spinning are indicated. The need for a relatively high solute concentration usually means that there is little choice of solvent. Particularly for coloured samples the presence of a vestigal resonance Raman effect must be tested by measurements with a variety of... 

Solids. Resonance Raman spectra of solid samples can be measured using pellets such as those described previously and rotating them using the technique depicted in Fig. 2-22a. This rotating device is available commercially from Raman instrument manufacturers. A special die with... 

Fig. 11.6 Resonance Raman spectra of compound III of horseradish peroxidase (0.2 mM) in 10 mM phosphate buffer, pH 7.8, containing 30% v/v methanol at — 10°C excited at three different wavelengths. Instrumental conditions spectral slit width 5 cm-1 laser power, 30 mW acquisition time, 40 min. Reproduced with permission from [139]...

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

---