Resonance Raman spectrum

As noted earUer these bridged compounds show intense MLCT(M28 to bridge n ) absorptions that typically faU in the visible region of the spectrum. With excitation into these bands the compounds show very significant resonance enhancement 

In normal Raman spectroscopy, the exciting frequency lies in the region where the compound has no electronic absorption band (Sec. I-l). In resonance Raman spectroscopy, the exciting frequency falls within the electronic band. In the gaseous phase, this tends to cause resonance fluorescence since the rotational-vibrational levels are discrete. In the liquid and solid states, however, these levels are no longer discrete because of molecular collisions and/or intermolecuiar interactions. If such a broad vibronic band is excited, it tends to give resonance Raman rather than resonance fluorescence spectra.  

The notations g, i, j, e, and v were explained in Sec. 1-20. Other notations are as follows s, another excited electronic state h ,the vibronic coupling operator dS /dQay M and being the electronic Hamiltonian and the ath normal coordinate of the electronic ground state, respectively E i and the energies 

In the case of totally symmetric modes, the product of the integrals t u) and (u y) in Eq. 21.2 is finite due to nonorthogonality of the vibrational wave functions at the electronic ground and excited states. On the other hand, these wave functions are nearly orthogonal for nontotally symmetric vibrations. Thus, only totally symmetric modes can derive Raman intensities via the A term. Nontotally symmetric and totally symmetric modes can gain Raman intensity via the B term as long as the ( u)(u 2a y)/(i —E ) in Eq. 21.3 is nonzero. In general, the B term contribution is small relative to the A term due in part to the additional denominator E —E.  

Spiro and co-workers carried out an extensive study on resonance Raman spectra of various heme proteins. As is shown in Fig. 1-18, ferrocyiochrome c exhibits two electronic transitions referred to as the Qq (or a) and B (or Soret) bands along with a vibronic side band (Q or /S) in the 400-600cm region. According to MO (molecular orbital) calculations on the porphine core of symmetry, the Qa and B transitions result from strong interaction between the iH( J ) Cg(7r ) and a uiir) transitions which have similar energies 

and 42 vibrations are expected to be polarized (p), depolarized (dp), and inversely polarized (tp ), respectively. These polarization properties, together with their vibrational frequencies, were used by Spiro and his coworkers to make complete assignments of vibrational spectra of the Fe-porphin skeletons of a series of heme proteins. They showed that the resonance Raman spectrum may be used to predict the oxidation and spin states of the Fe atom in heme proteins. For example, the Fe atom in oxyhemoglobin has been shown to be low-spin Fc(IIl). It should be noted that the A2y mode, which is normally Raman inactive, is observed under the resonance condition. Although the modes are rather weak in Fig. I-19, these vibrations are enhanced markedly and exclusively by the excitation near the B band since the A-term resonance is predominant under such condition. The majority of compounds studied thus far exhibit the A-term rather than the l -term resonance. A more complete study of resonance Raman spectra involves the observation of excitation profiles (Raman intensity plotted as a function of the exciting frequency for each mode), and the simulation of observed excitation proliles based on various theories of resonance Raman spectroscopy.  

In Sec. 1.20, we have shown that the depolarization ratio for totally symmetric vibrations is in the range 0 . For the A term to be nonzero, however, the term 

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]. 

In RR spectroscopy, the excitation line is chosen inside the electronic absorption band. This condition may cause thermal decomposition of the sample by local heating. To minimize thermal decomposition, several techniques have been developed. These include the rotating sample technique, the rotating (or oscillating) laser beam technique, and their combinations with low-temperamre techniques [21,26]. It is always desirable to keep low laser power so that thermal decomposition is minimal. This will also minimize photodecomposition, which occurs depending on laser lines in some compounds. 

As stated in the preceding section, the depolarization ratio (p ) is expected to be closed to i for totally symmetric vibrations. However, this value increases as the change in vibrational quantum number (Av) increases. For example, it is 0.48 for the tenth overtone of I2 in CCI4 [100]. 

Xi i is the anharmonicity constant corresponding to of a diatomic molecule (Sec. 1.3). 

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Fig. IV-14. Resonance Raman Spectra for cetyl orange using 457.9-nm excitation. [From T. Takenaka and H. Fukuzaki, Resonance Raman Spectra of Insoluble Monolayers Spread on a Water Surface, J. Raman Spectr., 8, 151 (1979) (Ref. 157). Copyright Heyden and Son, Ltd., 1979 reprinted by permission of John Wiley and Sons, Ltd.]...

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

Fig. XVI-5. Resonance Raman spectra of MDMA adsorbed on ZnO (a) in the presence of 100 torr of NH3 (b) after evacuation of the NH3 from the cell. [Reprinted with permission from J. F. Brazdil and E. B, Yeager, J. Phys. Chem., 85, 1005 (1981) (Ref. 79). Copyright 1981, American Chemical Society.]...

The pioneering use of wavepackets for describing absorption, photodissociation and resonance Raman spectra is due to Heller [12, 13,14,15 and 16]- The application to pulsed excitation, coherent control and nonlinear spectroscopy was initiated by Taimor and Rice ([17] and references therein). 

A beautiful, easy-to-read introduction to wavepackets and their use in interpreting molecular absorption and resonance Raman spectra. 

Infonuation about the haeme macrocycle modes is obtained by comparing the resonance Raman spectra of deoxyHb with HbCO. The d-d transitions of the metal are too weak to produce large enliancement, so the... 

Rossetti R, Nakahara S and Brus L E 1983 Quantum size effects In the redox potentials, resonance Raman spectra and electronic spectra of CdS crystallites In aqueous solution J. Chem. Phys. 79 1086... 

In an ambitious study, the AIMS method was used to calculate the absorption and resonance Raman spectra of ethylene [221]. In this, sets starting with 10 functions were calculated. To cope with the huge resources required for these calculations the code was parallelized. The spectra, obtained from the autocorrelation function, compare well with the experimental ones. It was also found that the non-adiabatic processes described above do not influence the spectra, as their profiles are formed in the time before the packet reaches the intersection, that is, the observed dynamic is dominated by the torsional motion. Calculations using the Condon approximation were also compared to calculations implicitly including the transition dipole, and little difference was seen. 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

Fig. 4.60. Comparison of resonance Raman spectra with and without tip enhancement for 0.5 monolayers of brilliant cresyl blue on a smooth gold film. The tip increased the total Raman intensity by a factor of approximately 15, when positioned at a tunneling distance of 1 nm. Several other bands were made visible as a result of the tip enhancement [4.306].

Figure 2.36 Resonance Raman spectra of (a) Rh2(l602)CMe4(PPh3)2 (b) Rh2(l802)CMe,((PPh )2 (c) Rh2(l602)C(CD3)4CPPh3)2. Recorded as KC1 discs at 80K,L = 363.8nm. (Reprinted with permission from J. Am. Chem. Soc., 1986,108, 518. Copyright (1986) American Chemical Society.)...

Figure 3.65 Resonance Raman spectra of [Plten HPtfenJjCljblCuCUk in a KC1 disk at 80 K, A = 568.2 nm. (Reproduced with permission from J. Chem. Soc., Dalton Trans., 1980, 2492.)...

Symmetry C2v C2h r Matrix infrared spectra (12 K)[17] Resonance Raman spectra (hot vapor) [76]... 

Ionic polysulfides dissolve in DMF, DMSO, and HMPA to give air-sensitive colored solutions. Chivers and Drummond [88] were the first to identify the blue 83 radical anion as the species responsible for the characteristic absorption at 620 nm of solutions of alkali polysulfides in HMPA and similar systems while numerous previous authors had proposed other anions or even neutral sulfur molecules (for a survey of these publications, see [88]). The blue radical anion is evidently formed by reactions according to Eqs. (5)-(8) since the composition of the dissolved sodium polysulfide could be varied between Na2S3 and NaaS with little impact on the visible absorption spectrum. On cooling the color of these solutions changes via green to yellow due to dimerization of the radicals which have been detected by magnetic measurements, ESR, UV-Vis, infrared and resonance Raman spectra [84, 86, 88, 89] see later. 

Electronic and Resonance Raman Spectra of Sulfiir-Containing Complexes (R. J. H. Clark)... 

Fig. 7. Low-temperature (77 K) resonance Raman spectra for A. vinelandii Fdl, T. thermophilus Fd, D. gigas Fdll, and ferricyanide-treated C. pasteurianuni Fd obtained with 488.0-nm excitation. Taken with permission from Ref. (17).

Fig. 8. Low-temperature (20 K) resonance Raman spectra of oxidized P. furiosus 3Fe Fd as a function of excitation wavelength (191).

In general, the resonance Raman spectra reveal strong structural similarity of the Fe " site in Rieske proteins and in proteins containing a 4-cysteine coordinated [2Fe-2S] cluster, while additional modes are observed for vibrations involving the Fe" site and the histidine ligands. 

Proniewicz LM, Odo J, Goral J, Chang CK, Nakamoto K. 1989. Resonance Raman spectra of dioxygen adducts of pillared cobalt cofacial diporphyrins. J Am Chem Soc 111 2105. 

Proniewicz LM, Paeng IR, Nakamoto K. 1991. Resonance raman spectra of two isomeric dioxygen adducts of iron(II) porphyrins and rr-cation radical and nonradical oxoferryl porphyrins produced in dioxygen matrixes Simultaneous observation of more than seven oxygen isotope sensitive bands J Am Chem Soc 113 3294. 

Strekas TC, Spiro TG. 1975. Resonance Raman spectra of superoxide-bridged binuclear complexes. p,-Superoxo-decacyanodicobaltate(5—) and /n-superoxo-decaamminedicobalt (5 +). Inorg Chem 14 1421. 

Figure 3.6. Resonance Raman spectra of the ground state of DMABN, DMABN- N, DMABN-A, DMABN-A obtained with 330nm excitation in methanol.

Figure 3.13. Resonance Raman spectra of Sj excited state trans-stilbene in decane at delay times indicated. The pump wavelength was 292.9 nm and the probe wavelength was 585.8nm. The vertical dashed lines illustrated the substantial spectral evolution of the 1565 cm compared to the 1239cm band. (Reprinted with permission from reference [56]. Copyright (1993) American Chemical Society.)...

Figure 3.21. Time resolved resonance Raman spectra of fluoranil (a) in acetonitrile (5.0 mM) at 20 ns time delay between pump and probe (Ap p 355 nm, Apj e 485 nm), (b) in chloroform (5.0 mM) at 20 ns delay between pump and probe (Ap n 355 nm, Apj e 416 nm). (c) Resonance Raman spectra of fluoranil radical anion in acetone (Apj te 441 nm). See text for more details. (Reprinted from reference [91]. Copyright (1997), with permission from Elsevier.)...

Figure 3.26. Picosecond Kerr gated time-resolved resonance Raman spectra obtained for HPDP in 50% H2O/50% MeCN mixed solvent with 267nm pump and 342nm probe (a) and 400 nm probe (b) wavelengths, respectively. (Reprinted with permission from reference [134]. Copyright (2005) American Chemical Society.)...

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