Raman spectroscopy spectra comparison

A second, independent spectroscopic proof of the identity of 4 as rans-[Mo(N2)2(weso-prP4) was provided by vibrational spectroscopy. The comparison of the infrared and Raman spectrum (Fig. 7) shows the existence of two N-N vibrations, a symmetric combination at 2044 cm-1 and an antisymmetric combination at 1964 cm-1, indicating the coordination of two dinitrogen ligands. In the presence of a center of inversion the symmetric combination is Raman-allowed and the antisymmetric combination IR allowed. The intensities of vs and vaK as shown in Fig. 2 clearly reflect these selection rules. Moreover, these findings fully agree with results obtained in studies of other Mo(0) bis(dinitrogen)... 

Infrared and Raman spectroscopy are in current use fo r elucidating the molecular structures of nucleic acids. The application of infrared spectroscopy to studies of the structure of nucleic acids has been reviewed,135 as well as of Raman spectroscopy.136 It was noted that the assignments are generally based on isotopic substitution, or on comparison of the spectrum of simple molecules that are considered to form a part of the polynucleotide chain to that of the nucleic acid. The vibrational spectra are generally believed to be a good complementary technique in the study of chemical reactions, as in the study76 of carbohydrate complexation with boric acid. In this study, the i.r. data demonstrated that only ribose forms a solid complex with undissociated H3B03, and that the complexes are polymeric. 

Brouwer and Wilbrandt have applied resonance Raman spectroscopy and calculations to questions of structure of amine radical cations [73]. Well-resolved Raman spectra of trialkylamine radical cations that are so short-lived that their electrochemical oxidation waves are irreversible may be obtained at room temperature in solution by photoionization and time-resolved detection. Comparison of the observed spectrum with calculations for various isomers provides a powerful method of answering structural questions. Density-functional calculations prove much easier to apply to open-shell species than Hartree-Fock calculations, which require cumbersome and expensive corrections to introduce suffieient electron correlation to eonsider questions like the charge distribution of disubstituted piperazine (1,4-diazacyclohexane) radical cations. The dimethyl- and diphenyl-substituted piperazine radical cations are delocalized, but charge is localized on one ArN unit of the dianisyl-substituted compound [73dj. 

Conclusive proof of the identity of the photoactive film on lead follows from the analysis of the photocurrent spectra. Figure 9(b) compares the spectrum of the anodic photocurrent with the absorption spectrum of the tetragonal form of PbO. The oxide film is sufficiently thin for the photocurrent to be a linear function of the absorption coefficient so that direct comparison of the photocurrent and absorption spectra is possible and it is clear from the coincidence of the two spectra that the film consists of tetragonal PbO. The results illustrate the sensitivity of photocurrent spectroscopy as a method for the identification of thin surface phases. In-situ Raman spectroscopy [24] and in-situ X-ray measurements [25] of the same system show no evidence for the formation of PbO unless the electrode is held at a constant potential for a time sufficient for a much thicker layer of oxide to be formed. By contrast, photocurrent spectroscopy is sufficiently sensitive to detect the formation of PbO on the much shorter timescale of a linear sweep measurement and quantitative estimates of the film thickness are feasible. Similar results have been obtained for the reduction of a-Pb02 in alkaline solution, where the existence of the tetragonal form has also been established from the photocurrent spectra [26]. 

Fig. 17. Comparison between the spectrum of the iron heme in the /3 subunits (top) and in the a subunits (bottom) from iron-cobalt hybrid hemoglobins. Contributions from the cobalt-containing hemes are not present in the spectrum with this excitation wavelength (441.6 nm). [From D. L. Rousseau and J. M. Friedman, in "Biological Applications of Raman Spectroscopy (T. G. Spiro, ed.), Vol. 3, p. 133. Wiley, New York, 1988.]...

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