Raman spectroscopy selection rules, 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)... 

Some characteristics of, and comparisons between, surface-enhanced Raman spectroscopy (SERS) and infrared reflection-absorption spectroscopy (IRRAS) for examining reactive as well as stable electrochemical adsorbates are illustrated by means of selected recent results from our laboratory. The differences in vibrational selection rules for surface Raman and infrared spectroscopy are discussed for the case of azide adsorbed on silver, and used to distinguish between "flat" and "end-on" surface orientations. Vibrational band intensity-coverage relationships are briefly considered for some other systems that are unlikely to involve coverage-induced reorientation. 

A particularly salient example of the complementarity of normal Raman spectroscopy with other techniques is expressed in a recent publication of the combined data from infrared, normal Raman, SERS, SEHRS, and theoretical predictions for one molecule. First, ab initio theoretical predictions were made for the vibrational characteristics of fran5-l,2-bis(4-pyridyl)ethylene (BPE) at the Hartree-Fock 6-31G level. When the spectra were collected, comparisons were made between the theoretical and experimental results as well as among the different spectra. Based on the known selection rules for each spectroscopy and the matching of wavenumber shifts to theoretical predictions, all vibrational bands were assigned. 

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