Resonance Raman spectroscopy coupling

Infrared and Raman spectroscopy each probe vibrational motion, but respond to a different manifestation of it. Infrared spectroscopy is sensitive to a change in the dipole moment as a function of the vibrational motion, whereas Raman spectroscopy probes the change in polarizability as the molecule undergoes vibrations. Resonance Raman spectroscopy also couples to excited electronic states, and can yield fiirtlier infomiation regarding the identity of the vibration. Raman and IR spectroscopy are often complementary, both in the type of systems tliat can be studied, as well as the infomiation obtained. 

The first investigation of the phonon modes in binary InN was an extrapolation of the Gai-xInxN (0 < x < 1) alloy modes in reflection towards the binary compound [1], A typically high free carrier concentration in the mid 1020 cm 3 range controls the absorption (Drude absorption) in the infrared and must also account for the broadened Reststrahlen band in pure InN films (e.g. in [1]). In this case infrared active phonons couple to the plasma of the free electrons forming phonon-plasmon coupled modes [10,11], However, layers of low carrier concentration have been achieved and pure LO phonon energies have been derived in Raman spectroscopy. Resonant Raman spectroscopy at 514 nm has been performed, assigning five of the six Raman allowed zone centre phonon modes [8,9] (TABLE 1). 

Resonance Raman and NMR Studies. The major support to the protonation hypothesis is presently based on the recent application of resonance-Raman spectroscopy. (For recent reviews, see refs. 217-219.) The method uses an incident beam which is in resonance with the absorption of the retinyl chromophore. This results in the selective enhancement of the Raman cross sections coupled with the chromophore, relative to the very weak, non-resonant, modes of the opsin. Characteristic spectra are shown in Fig. 6. Early evidence for protonation came from the observation of a close similarity between the C=N vibrational frequency in rhodopsin and in a model protonated Schiff base (220). More conclusive arguments were provided by Oseroff and Callender, who carried out experiments at low temperatures in order to control sample photoability (221). It was observed that deuteration shifts the C=N vibration frequency from 1655 cm- to 1630 cm-- -, both in the pigment and in a model protonated Schiff base. 

Online coupling of surface-enhanced resonance Raman spectroscopy and IPC proved valuable for the identification of basic dyes [124]. Circular dichroism spectroscopy is an extraordinary technique for selective detection of compounds possessing optically active adsorption bands and was successfully coupled to IPC of steroids [125]. Table 12.4. summarizes the most important features and parameters to be compared when selecting a detection mode for an IPC application. 

Seifar, R.M. et al. At-line coupling of surface-enhanced resonance Raman spectroscopy and reversed-phase ion-pair chromatography. Ana/. Commun. 1999, 36, 273-276. 

The vibronic coupling between the chromophores of Zn(4-TRPyP) was studied by resonance Raman spectroscopy using six laser lines in the 450-515-nm range (180), covering the spectral range of the Soret, Ru (7jt) (ptt )bpy and... 

Metal-ligand modes were identified by resonance Raman spectroscopy, and assigned after a normal coordinate analysis, for Mn2(0)(0Ac)2(bipy)2 (H20)2.24° Resonance Raman spectra of MnN(P), where P = a range of porphyrins, included vMn=N near 1050 cm-1.241 The IR spectra of Min(P)Cl, Mn(P), where M111 = Mn, Fe Mn = Co, Ni, Cu, Zn, P = meso-tetra-(4-myristyloxy-phenyl)porphyrin, included vMnN (coupled with a porphyrin deformation mode) at 250 cm 1, and vMninCl 320 cm 1.242... 

These phenomena can be reliably traced back to Jahn-Teller and strain distortion combined to unquenched orbital angular momentum due to spin-orbit-coupling in the metalloporphyrins. The Jahn-Teller distortion has been also studied by resonance Raman spectroscopy. " ... 

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