Spectroelectrochemistry Raman

Raman spectroelectrochemistry has been reviewed in detail (65, 66). The type of cell used for spectroelectrochemistry depends to some extent on the optical layout of the Raman experiment. The main optical layouts in conventional Raman spectroscopy are front incident and collection mode, 180° backscattering, and ATR mode. For most solution phase applications of Raman spectroeleclrochemistry, a three-electrode cell for bulk electrolysis is used and a number of such cells have been described (67). The conventional OTTLE cell described for electronic spectroscopy can be used in Raman spectroelectrochemistry. However, this cell can suffer from solvent interference in non-aqueous media Thin layer cells like those desaibed for IR are also frequendy used (66). 

A more recent advance in Raman spectroscopy which has increased its versatility is Raman confocal microscopy. In confocal microscopy, out-of-focus infonnatiou, which contributes to the overall image in conventional microscopy, is eliminated by means of a 

The overriding drawback of Raman spectroscopy is that Raman scatter is fundamentally a weak phenomenon. Resonance Raman spectroscopy and surface enhanced Raman spectroscopy (SERS) are two methods which can be exploited in a spectroelectrochemical experiment to enhance the signal and increase the selectivity of the signal. 

In resonance Raman spectroscopy (73), the Franck Condon modes of a chromophore can be resonantly enhanced by up to seven orders of magnitude by using excitation wavelengths that are coincident with the absorbances under interrogation. The theory behind this condition is complex (74) and beyond the scope of this chapter. Employing the resonance condition in spectroelectrochemistry provides a unique aud powerful opportunity to unequivocally ideutily new optical transitions resulting from electrode reactions. 

Resonance Raman spectroelectrochemistry was carried out on [Ru(bpy )2(box)] + and the osmium analogue in which the bipyridyl units were perdeuteriated [Os(dg-bpy)2(box)]+ by holding the cell potential beyond the first oxidation step for each sample. The resonance Raman spectra of [Rn(bpy)2(box)p+ and [Os(bpy)2(box)] are in essence analogous. This implies that the bipyridyl unit does not participate in the new optical transition in the oxidized complex and therefore confirmed that for both M(bpy) containing complexes the NIR band is a phenolate (tc) to M(III) (djt) Ugand to metal charge transfer LMCT transition. This example also serves to illustrate how a simple synthetic modification such as deuteriation can yield detailed information on electron transfer processes. If the bipyridyl unit were involved in the optical transition, shifts of between 30 and 60 cm would have been observed between the deuteriated and non-deuteriated spectra. 

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Radical ions, 33, 44 Raman spectroelectrochemistry, 45 Randles-Sevcik equation, 31 Rate constant, 12, 18 Rate determining step, 4, 14 Reaction mechanism, 33, 36, 113 Reaction pathway, 4, 33 Reaction rate, 12 Receptor-based sensors, 186 Redox recycling, 135... 

Jeanmaire, D. L. and Van Duyne, R. P. (1977) Surface Raman spectroelectrochemistry Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode. J. Electroanal. Chem., 84, 1—20. 

Itoh T, McCreery RL (2002) In situ Raman spectroelectrochemistry of electron transfer between glassy carbon and a chemisorbed nitroazobenzene monolayer. J Am Chem Soc 124 (36)40894-10902... 

Raman spectroelectrochemistry (71, 72) is a field in which one studies electrogenerated species on electrode surfaces, in electrode diffusion layers and bulk solution by Raman spectroscopy. Thus, the surface-enhanced Raman scattering (SERS) discussed in the preceding section is part of Raman spectroelectrochemistry. Here, we discuss Raman spectroscopic studies on electrogenerated species in bulk solution and in electrode diffusion layers. Since no enhancement from SERS is expected and since the concentrations of these electrogenerated species are rather low, it is imperative to take advantages of resonance Raman (RR) scattering (Section 1.15). 

Figure 3-19 Resonance Raman spectroelectrochemistry cells and back scattering geometry. (A) Controlled potentional electrolysis cell (B) sandwich cell for semi-infinite diffusion conditions. (Reproduced with permission from Ref. 73. Copyright 1975 American Chemical Society.)...

Surface-Enhanced Raman Spectroscopy (SERS) Raman Spectroelectrochemistry Time-Resolved Raman (TR-) Spectroscopy Matrix-Isolation Raman Spectroscopy 2D Correlation Raman Spectroscopy Raman Imaging Spectrometry Nonlinear Raman Spectroscopy References... 

In situ Surface Enhanced Raman Spectroelectrochemistry (SERS) [vii]... 

Wertz provides a good inorganic example of Raman spectroelectrochemistry in which a series of ruthenium polyazine complexes were studied in varying redox states. The series of complexes and redox states studied were [Ru(bpm)3] " (n = 0 4), [Ru(bpz)(bpy)2] " [n = 0-3), [Ru(bpy)2(bpz)] " (n = 0-3), [Ru(bpz)3] " (n = 0 3), (bpm = 2,2 -bipyrimidine, bpz = 2,2 -bipyrazine, bpy = 2,2 -bipyridine) where n is the number of electrons added to the complex. Resonance Raman spectra are recorded at each redox state to investigate the identity of the redox orbital for the series of complexes. Figure 19 shows a... 

Jeanmaire, D. L. and Van Duyne, R. P. (1977). Surface Raman spectroelectrochemistry Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode. J. Electroaml. Chem. 84 1-20. Albrecht, M. G. and Creighton, J. A. (1977). Anomalously intense Raman spectra of pyridine at a silver electrode. J. Am. Chem. Soc. 99 5215-5217. Van Duyne, R. P. (1979). In Chemical and biochemical applications of lasers, Moore, C. B. (Ed.), academia press. New York, pplOl-185,... 

Shegai T, Vaskevich A, Rubinstein I, Haran G (2009) Raman spectroelectrochemistry of molecules within individual electromagnetic Hot spots. J Am Chem Soc 131(40) 14390-14398... 

Fig. 1. Typical Raman spectroelectrochemistry equipment system. WE, working electrode CE, counter electrode RE, reference electrode...

D. L. (eanmaire and R. P. Vanduyne, Sur-fiace Raman Spectroelectrochemistry. I. Heterocyclic, Aromatic, and Aliphatic-Amines Adsorbed on Anodized Silver Electrode,... 

A very elegant approach overcoming this problem has been proposed based on a channel flow cell geometry with downstream detection (Fig. II.6.2d). The potential of the electrode is stepped during steady-state flow of the solution across the electrode. A downstream UVA is detector system is then employed to measure the time dependence of the concentration profile formation at the electrode surface. A computer program is employed to relate the time-dependent absorbance signal to the concentration profile of reactant and product at the electrode surface. Alternatively, direct measurement of the concentration profiles at the electrode surface has also been reported based on confocal Raman spectroelectrochemistry [16]. 

Bonhomme, F., J. C. Lass gues, and L. Servant. 2001. Raman spectroelectrochemistry of a carbon supercapacitor. Journal of the Electrochemical Society 148 E450-E458. 

Figure 1.8 In situ Raman spectroelectrochemistry data for the G and G bands of graphene excited by 2.33 eV laser irradiation. The heavy black trace is for t =0 applied voltage. (Adapted from Ref. [33].)...

Frank, O., Dresselhaus, M.S., and Kalbac, M. (2015) Raman spectroscopy and in-situ Raman spectroelectrochemistry of isotopically engineered graphene systems. Acc. Chem. Res., 48(1), 111-118. 

Kalbac, M., Kavan, L., Zukalova, M., and Dunsch, L. (2006) The identification of dispersive and non-dispersive intermediate frequency modes of HiPco single walled carbon nanotubes by in situ Raman spectroelectrochemistry. Phys. Status Solidi, 243, 3134-3137. 

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