Resonance enhancement

REMPI Resonance-enhanced multi- Laser-induced ionization ... 

Nesselrodt D R, Potts A R and Baer T 1995 Stereochemical analysis of methyl-substituted cyclohexanes using 2+1 resonance enhanced multiphoton ionization Anal. Chem. 67 4322-9... 

Resonance Raman Spectroscopy. If the excitation wavelength is chosen to correspond to an absorption maximum of the species being studied, a 10 —10 enhancement of the Raman scatter of the chromophore is observed. This effect is called resonance enhancement or resonance Raman (RR) spectroscopy. There are several mechanisms to explain this phenomenon, the most common of which is Franck-Condon enhancement. In this case, a band intensity is enhanced if some component of the vibrational motion is along one of the directions in which the molecule expands in the electronic excited state. The intensity is roughly proportional to the distortion of the molecule along this axis. RR spectroscopy has been an important biochemical tool, and it may have industrial uses in some areas of pigment chemistry. Two biological appHcations include the deterrnination of helix transitions of deoxyribonucleic acid (DNA) (18), and the elucidation of several peptide stmctures (19). A review of topics in this area has been pubHshed (20). 

Fig. 25. Room temperature Raman spectra for purified single-wall carbon nanotubes excited at five different laser wavelengths, showing evidence for the resonant enhancement effect. As a consequence of the ID density of states, specific nanotubes (n, m) are resonant at each laser frequency [195].

Quantum effects are observed in the Raman spectra of SWCNTs through the resonant Raman enhancement process, which is seen experimentally by measuring the Raman spectra at a number of laser excitation energies. Resonant enhancement in the Raman scattering intensity from CNTs occurs when the laser excitation energy corresponds to an electronic transition between the sharp features (i.e., (E - ,)" type singularities at energy ,) in the ID electronic DOS of the valence and conduction bands of the carbon CNT. 

Resonance Enhanced Photodissociation FeO States Below the Dissociation Limit... 

Unfortunately, predissociation of the excited-state limits the resolution of our photodissociation spectrum of FeO. One way to overcome this limitation is by resonance enhanced photodissociation. Molecules are electronically excited to a state that lies below the dissociation limit, and photodissociate after absorption of a second photon. Brucat and co-workers have used this technique to obtain a rotationally resolved spectrum of CoO from which they derived rotational... 

Figure 7. Resonance enhanced (1 + 1) photodissociation spectrum and rotational assignments of the Il7/2 (v = 8) (v" = 0) band of FeO. Numbers indicate / for each line the...

Figure 10. Vibrational spectra of the [HO—Fe—CHs] insertion intermediate in the O—H stretching region. Spectra are obtained by monitoring loss of argon from IR resonance enhanced photodissociation of the argon-tagged complexes [HO—Fe—CH3] (Ar) (n — 1,2).

Figure 11. Infrared resonance enhanced photodissociation spectrum of V (OCO)5 obtained by monitoring loss of CO2. The antisymmetric stretch of outer-shell CO2 is near 2349 cm (the value in free CO2, indicated by the dashed vertical line). The vibration shifts to 2375 cm for inner-shell CO2.

Figure 16. Experimental and calculated IR resonance enhanced photodissociation spectra of Fe" (CH4)3 and Fe" (CH4)4. Experimental spectra were obtained by monitoring loss of CH4. Calculated spectra are based on vibrational frequencies and intensities calculated at the B3LYP/ 6-311+G(d,p) level. Calculated frequencies are scaled by 0.96. The calculated spectra have been convoluted with a 10-cm full width at half-maximum (FWHM) Gaussian. The D2d geometries of Fe (CH4)4 are calculated to have very similar energies, and it appears that both isomers are observed in the experiment.

On the other hand, we cannot ignore drawbacks in observing fourth-order responses. The desired response is always weak due to the high optical order. The damage threshold of the interface to be analyzed is severe with intense irradiation. The difficulty has been overridden by one-photon resonant enhancement of Raman-pump efficiency. The observable range of materials is somewhat limited as a result. There is still much room for technical improvements and the author is optimistic for the future. 

Ishibashi, T. and Onishi, H. (2004) Multiplex sum-frequency spectroscopy with electronic resonance enhancement. Chem. Lett., 33, 1404-1407. 

The TED and XRD patterns revealed that the deposit is not amorphous carbon but nanocrystalline diamond. Nonetheless, the 514-nm excited Raman spectra do not exhibit a clear diamond peak at 1332 cm though the peak due to the sp -bonded carbon network appears at 1150 cm The Raman cross section of the sp -bonded carbon network with visible excitation is resonantly enhanced [43, 48-50]. It consequently makes the 1332 cm diamond peak overlap with the peaks due to sp -bonded carbon. 

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