Resonance Raman process

Auger Resonant Raman Processes Effects of the Partial Density of Unoccupied Electronic States on Resonant KLL Auger Spectra in... 

AUGER RESONANT RAMAN PROCESSES EFFECTS OF THE PARTIAL DENSITY OF UNOCCUPIED ELECTRONIC STATES ON RESONANT KLL AUGER SPECTRA IN Cu AND Ni METALS... 

Fig. 9. 23 (a) Representation of a double resonance Raman process that gives rise to the D band, (b) Schematic illustration of the atomic stmcture of the edges, (c) Double resonance mechanism for an armchair edge [50]... 

The absorption intensity of the 0-1 vibronic sideband is entirely borrowed by HT coupling. The observation that this 0-1 transition is of comparable intensity to the 0-0 transition suggests the feasibility of resonance Raman processes in which both the absorption and emission moments are borrowed. This second-order HT coupling displays itself in the appearance of first overtones and combination bands of non-totally symmetric modes. These are observed extensively in the haem proteins 35). 

No doubt, the present author has his own private consensus which, in spite of his efforts, may inject itself into the review. In order to offset such an undesirable bias, as much as possible, and perhaps putting the cart before the horse, the author will state here his own conclusions and beliefs I am convinced that electric field amplification and enhanced emission near SERS-active surfaces due to resonating metal excitations (surface-plasmon polaritons, plasmonlike modes, shape resonances, or electron-hole pairs) is an active mechanism in most of the systems studied. However, in most systems, this contribution, though an important one, is minor compared to the total enhancement possible in SERS. The major mechanism, in my opinion, must be a resonance mechanism, in the sense of a resonance Raman process, i.e., a mechanism by which a part of the system (molecule, molecule-metal atoms, metal surface) becomes a strong scatterer by virtue of its large resonance polarizability and not as a result of strong fields exerted by the other parts of the system . 

Basically, this set of models claims that SERS is a result of a resonance Raman process, where the molecule avails itself of the unoccupied states of the metal, or vice versa. Thus one can envisage a virtual intermediate transition to occur not between pure molecular states, but between a molecular and a metal state. This model has the advantage of a clear chemical picture, but it does not easily lend itself to rigorous calculations leading to quantitative predictions. 

Resonance Raman and antisymmetric scattering are involved in a novel technique involving spin-flip Raman transitions in paramagnetic molecules that can function as Raman electron paramagnetic resonance. Figure 3.2a shows a conventional vibrational Stokes resonance Raman process, while 3.2b and 3.2c show the polarization characteristics of the two distinct spin-flip Raman processes for scattering at 90°... 

The last scheme in Fig. 5.15c, named A-type OODR, represents a stimulated resonant Raman process where the molecules are coherently transferred from level 11) to levels m) by absorption of the pump laser and stimulated emission by the probe laser. 

Ramsey s method for the observation of narrow radiofre-guency (rf) resonances is well known from atomic and molecular beam experiments . In this contribution, we demonstrate the occurence of similar Ramsey resonances in an atomic vapor due to collisional velocity diffusion of sublevel coherence within an optical Doppler distribution. This new phenomenon is observed using coherent resonance Raman processes to optically induce and detect Zeeman coherence in the Sm A=570.7 nm J=1-J =0 transition. 

The detailed studies show that the saturation of the common level, as discussed above, is not the only coupling mechanism. The interaction of the atom with a light wave generates an induced dipole moment which is at small intensities proportional to the field amplitude. At higher intensities the nonlinear terms in the induced polarization become important. If two waves with frequencies and simultaneously act in resonance with the atom, these nonlinear terms produce sum and difference frequencies For two transitions which share a common level the difference frequency - W2 is in resonance with the atomic transition b c (2 2 - 3 2) and will therefore modulate the atomic polarization at the frequency - 0)2 The phenomenon can be regarded as a resonant Raman process where the 0.63 ym transition generates the Stokes line at X = 1.15 ym and both waves force the electronic polarization to oscillate at the difference frequency (see Sect.9.4). 

The Resonance Raman Process and Duschinsicy Mixing Effect... 

The scattering intensity of the resonance Raman process that carries the molecule from an initial vibrationless wi = H2 = 0 to final vibrational state n = (ni, >12) (in the ground electronic state 0) by absorption at frequency v and emission at hv = hv—nhcD is given by Refs [219, 293-296]... 

This effect is illustrated in Figure 3. Such an effect would be predicted since the electrode potential controls the metal energy state (Fermi level) which would be involved in a resonance Raman process. When the laser energy is changed, a compensating change in the electrode potential (Fermi level) could reestablish the resonance condition. 

Enhanced Scattering in a Surface-Enhanced Resonance Raman Process... 

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