Raman laser spectroscopy

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Laser Raman spectroscopy and Si ft-nmr spectroscopy have been used to examine direcdy the stmcture of sdicate species in solution (34—41). 

Chemical Properties. MSA combines high acid strength with low molecular weight. Its pK (laser Raman spectroscopy) is —1.9, about twice the acid strength of HCl and half the strength of sulfuric acid. MSA finds use as catalyst for esterification, alkylation, and in the polymerisation and curing of coatings (402,404,405). The anhydrous acid is also usefijl as a solvent. 

The mechanisms of lead corrosion in sulfuric acid have been studied and good reviews of the Hterature are available (27—30). The main techniques used in lead corrosion studies have been electrochemical measurements, x-ray diffraction, and electron microscopy. More recendy, laser Raman spectroscopy and photoelectrochemistry have been used to gain new insight into the corrosion process (30,31). 

Laser Raman Spectroscopy and Its Application to the Study of Adsorbed Species... 

Laser Raman spectroscopy as it is applied to the study of surface adsorbed.species involves a number of experimental problems such as fluorescence, weak Raman lines, and interfering plasma lines. Techniques of overcoming these problems have been continually improved and good... 

Fia. 13. (a) Raman spectrum of a pretreated Cab-O-Sil disk recorded using a laser beam expander (b) infrared spectrum of a newly pressed Cab-O-Sil disk. From Hendra and Gilson, Laser Raman Spectroscopy, p. 186. Wiley, New York, 1970. 

There are, at present, two overriding reasons an experimentalist would choose to employ laser Raman spectroscopy as a means of studying adsorbed molecules on oxide surfaces. Firstly, the weakness of the typical oxide spectrum permits the adsorbate spectrum to be obtained over the complete fundamental vibrational region (200 to 4000 cm-1). Secondly, the technique of laser Raman spectroscopy is an inherently sensitive method for studying the vibrations of symmetrical molecules. In the following sections, we will discuss spectra of pyridine on silica and other surfaces to illustrate an application of the first type and spectra of various symmetrical adsorbate molecules to illustrate the second. 

Earlier in this review, the relationship between the Raman and infrared spectra of molecules possessing high or low symmetry was considered. It was indicated that for molecules possessing a center of symmetry, no vibration is active in both the Raman and infrared spectra. Several adsorbates in this category and one of intermediate symmetry have been studied by laser Raman spectroscopy (Table IX), and most of these spectra are considered in this section. 

A Summary of Adsorbate-Adsorbent Systems Investigated Using Laser Raman Spectroscopy... 

Though as yet in its infancy, the application of laser Raman spectroscopy to the study of the nature of adsorbed species appears certain to provide unusually detailed information on the structure of oxide surfaces, the adsorptive properties of natural and synthetic zeolites, the nature of adsorbate-adsorbent interaction, and the mechanism of surface reactions. 

Loader, E. J., Basic Laser Raman Spectroscopy, pp. 32-35. Heyden, London, 1970. 

Laser Raman spectroscopy, 293-341, see also Raman spectroscopy... 

These models are designed to define the complex entrance effects and convection phenomena that occur in a reactor and solve the complete equations of heat, mass balance, and momentum. They can be used to optimize the design parameters of a CVD reactor such as susceptor geometry, tilt angle, flow rates, and others. To obtain a complete and thorough analysis, these models should be complemented with experimental observations, such as the flow patterns mentioned above and in situ diagnostic, such as laser Raman spectroscopy. 

The vibrations of molecular bonds provide insight into bonding and stmcture. This information can be obtained by infrared spectroscopy (IRS), laser Raman spectroscopy, or electron energy loss spectroscopy (EELS). IRS and EELS have provided a wealth of data about the stmcture of catalysts and the bonding of adsorbates. IRS has also been used under reaction conditions to follow the dynamics of adsorbed reactants, intermediates, and products. Raman spectroscopy has provided exciting information about the precursors involved in the synthesis of catalysts and the stmcture of adsorbates present on catalyst and electrode surfaces. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Bruckner, A. and Kondratenko, E. (2006) Simultaneous operando EPR/UV-vis/laser-Raman spectroscopy - A powerful tool for monitoring transition metal oxide catalysts during reaction, Catal. Today, 113, 16. 

---