Other Types of Raman Spectroscopy

Advancements in tunable lasers led to several new Raman s K ctroscopic methods in llie early 1970s. A brief discussion of the applications of some of these techniques follow. s. 

Resonance Raman scattering refers to a phenomenon in which Raman line intensities are greatly enhanced by excilalion with wavelengtbs that closely approach that of an electronic absorption band of an analyte. Under this circumstance, the magnitudes of Raman 

Perhaps the most important application of resonance Raman spectroscopy has been to the study ol biological molecules under physiologically significant conditions that is. in the presence of water and at low to moderate concentration levels.. - s an example, the technique has been useil lo determine the oxidation state and spin of iron atoms in hemoglobin and cytochrome c. In these molecules, the lesonance Raman bands are due solelv to ibrational modes of the tetra- 

Time-resobed resonance Raman spectrometry is a technique that allows collection of Raman spectra of excited state molecules. It has heen used lo study in-lermediaies in enzyme reactions, the spectra of carotenoid excited slates, ultrafasi electron transfer steps, and a variety of olher biological and bioinoiganic processes, I inie discrimination methods have been used to overcome a major limitation of resonance Raman spectroscope, namelv. fluorescence interference either by the analyte itself or by other species present in the sample. 

Several sample-handling techniques are employed for SERS, In one technique, colloidal silver or gold particles are suspended in a dilute solution (usually aqueous) of the sample. The solution is then held or flowed through a narrow glass tube while it is excited by a laser beam. In another method, a thin film of colloidal metal panicles is deposited on a glass slide and a drop or two of the sample solulion spotted on the film. The Raman spectrum is then obtained in the usual manner. Alternatively, the satnple may be deposited electrolytically on a roughened metal electrode, which is then removed from the solulion and exposed to the laser excitation source. 

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D Other Types of Raman Spectroscopy 493 Questions and Problems 495... 

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