UV Raman laser spectroscopy

Yu et al. [252] successfully employed UV Raman laser spectroscopy for the characterization of the framework vibration range of zeolites A,X, Y, MOR, L, and Beta. UV Raman laser spectroscopy proved to be advantageous in that it was much less disturbed by fluorescence than the conventional Raman laser technique. The authors claimed that x-membered rings (xMR) in the structures were manifested by absorptions in the wavenumber ranges (in cm 0 470-530 (4MR), 370-430 (5MR), 290-410 (6MR) and 220-280 (8MR). The method was also used for the characterization of TS-1, [Fe]ZSM-5, [V]MCM-41 and in synthesis studies (vide infra). 

Replacement of Si by Fe in silicalite-1, resulting in [Si,Fe]MFI, gave rise to an IR-active mode at 1015 cm and a Raman-active mode at 1020 cm" (cf.Ref. [324] and Volume 1, Chapter 7, page 220, of the present series). These modes were assigned to vibrations of (-O-ljSi-OH entities polarized by adjacent Fe + in the structure in analogy with what was discussed for the appearance of the 960 cm band in [Si,Ti]MFI (vide supra). The region of framework vibrations of [Fe]ZSM-5 was also investigated by UV Raman laser spectroscopy (cf. Yu et al., [339]). 

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. 

An interesting and powerful new development in Raman spectroscopy of catalysts is the use of a UV laser to excite the sample. This has two major advantages. First, the scattering cross section, which varies with the fourth power of the frequency, is substantially increased. Second, the Raman peaks shift out of the visible region of the spectrum where fluorescence occurs. The reader is referred to Li and Stair for applications of UV Raman spectroscopy on catalysts [40]. 

A promising recent development in the study of nitrenium ions has been the introduction of time-resolved vibrational spectroscopy for their characterization. These methods are based on pulsed laser photolysis. However, they employ either time resolved IR (TRIR) or time-resolved resonance Raman (TRRR) spectroscopy as the mode of detection. While these detection techniques are inherently less sensitive than UV-vis absorption, they provide more detailed and readily interpretable spectral information. In fact, it is possible to directly calculate these spectra using relatively fast and inexpensive DFT and MP2 methods. Thus, spectra derived from experiment can be used to validate (or falsify) various computational treatments of nitrenium ion stmctures and reactivity. In contrast, UV-vis spectra do not lend themselves to detailed structural analysis and, moreover, calculating these spectra from first principles is still expensive and highly approximate. 

The electrochemistry and cristallography of the nickel oxides have been extensively investigated in connection with the improvement of storage batteries . In-situ UV/visible reflectance spectroscopy and laser raman spectroscopy of the... 

The most conventional excitation source for Raman spectroscopy, a 514-nm Ar-ion laser, is known to cause a strong fluorescence during the analysis of ND samples. Compared to visible Raman, UV-Raman analysis offers a stronger diamond signal due to the resonance enhancement effect [85]. It is therefore preferred to use UV (244 and 325 nm) excitations for the analysis of ND powders. 

In the visible Raman spectra the cross section of the sp phase is much higher (50-250 times for 514.5 nm) than that of the sp phase. Hence UV Raman spectroscopy (Renishaw 2000 system) with a He- Cd laser (325 nm wavelength) was used for vibrational studies of the sp -bonded carbon phase. The resulting spectra recorded at different points at the surface besides the D- and G-band demonstrated a new feature in the range 1328 1332cm , which corresponds to the CVD-deposited nanocrystalline-sized diamonds (Figure 3.9b). The curve shape analysis of this band, i.e. its peak position and width provides information about the size of the CVD-deposited diamond crystallites [30]. With diamond size decreasing from 1000 nm to... 

Vibrational frequencies for example result from the appUcation of infrared, laser-induced fluorescence, Raman, and Raman resonance spectroscopy. Spectroscopy in the visible and near-UV regions yields information on electronic transitions. Electron spin resonance spectroscopy is used in determining the geometric and electronic structure. These methods were applied to study the gaseous species trapped at low temperatures in a solid inert rare gas matrix (matrix isolation technique) as well as in the free state. 

Because of the advantages mentioned in the preceding section, resonance Raman (RR) spectroscopy has been applied to vibrational studies of a number of inorganic as well as organic compounds. It is currently possible to cover the whole range of electronic transitions continuously by using excitation lines from a variety of lasers and Raman shifters [26]. In particular, the availability of excitation lines in the U V region has made it possible to carry out UV resonance Raman (UVRR) spectroscopy [104]. 

UV-vis, laser Raman (under resonance conditions), and X-ray absorption spectroscopy have been the dominant techniques used both to determine the maximum level of titanium incorporation in the framework, and also to identify the structure of the species formed by adsorption of H2O2 on titanium centers within the TS-1 framework. Unfortunately, the majority of these techniques are not quantitative, and efforts have rarely been made to quantitatively cross-correlate the results from the different characterization methods. It is therefore difficult for the researcher to read the literature in this area and arrive at a conclusion. Research to resolve these inconsistencies would be beneficial to the field. 

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