SFG vibrational

Viggiano A A, Morris R A and Paulson J F 1994 Effects of f and SFg vibrational energy on the rate constant for charge transfer between and SFg int. J. Mass Spectrom. ion Processes 135 31-7... 

In SFG vibrational spectroscopy, cOi is usually fixed in the visible region and CO2 is scanned in the infrared region. In the most widely used geometry, the two laser... 

Hyper-Raman spectroscopy is not a surface-specific technique while SFG vibrational spectroscopy can selectively probe surfaces and interfaces, although both methods are based on the second-order nonlinear process. The vibrational SFG is a combination process of IR absorption and Raman scattering and, hence, only accessible to IR/Raman-active modes, which appear only in non-centrosymmetric molecules. Conversely, the hyper-Raman process does not require such broken centrosymmetry. Energy diagrams for IR, Raman, hyper-Raman, and vibrational SFG processes are summarized in Figure 5.17. 

Figure 7. Total internal reflection sum frequency generation (TIR-SFG) vibrational spectroscopy of high-pressure room temperature adsorption of carbon monoxide on PVP-protected Pt cube monolayers and calcined (373 K, 3h) monolayers [27], The infrared spectra demonstrate CO is adsorbed at atop sites, but is considerably red-shifted on the PVP-protected Pt cubes. After calcination, the atop frequency blueshifts to 2085 cm in good agreement with CO adsorption on Pt(l 0 0) at high coverages [28], (Reprinted from Ref [27], 2006, with permission from American Chemical Society.)...

The use of neutron reflectivity at liquid interfaces, which is a method sensitive to both surface roughness and surfactant layer thickness, was reviewed with the examples of polydimethylsiloxane-surfactant layers.633 Sum-frequency generation (SFG) vibrational spectroscopy was applied to study surface restructuring behavior of PDMS in water in an attempt to understand antifouling properties of silicones.6 ... 

To acquire an SFG vibrational spectrum of adsorbate molecules on a metal catalyst, two (picosecond) laser pulses are spatially and temporally overlapped on the sample (Fig. 5). One input beam is in the visible range at fixed frequency (covis), and the second one is tunable in the mid-IR region (giir) to probe the vibrational... 

Rupprechter G, Unterhalt H, Morkel M, GaUetto P, Hu L, Freund H-J (2002) SFG vibrational spectroscopy at solid-gas interfaces CO adsorption on Pd model catalysts at ambient pressure. Surf Sci 502-503 109... 

Figure 5 shows the SFG vibrational spectra of carbon monoxide obtained at 10 -700 Torr of CO and at 295 K. When the clean Pt(lll) surface was exposed to 10 L (1 L=10 Torr sec) of CO in UHV, two peaks at 1845 cm and 2095 cm were observed which are characteristic of CO adsorbed at bridge and atop sites. LEED revealed that a c(4 X 2) structure was formed in which an equal number of carbon monoxide molecules occupied atop and bridge sites [15]. Such results are in agreement with previous HREELS [16] and reflection-absoiption infrared spectroscopy (RAIRS) [17] studies. ITie much higher relative intensity of atop bonded CO to bridge bonded CO in the SFG spectra is due to the specific selection rule for the SFG process [18]. As mentioned earlier, SFG is a second order, nonlinear optical technique and requires the vibrational mode under investigation to be both IR and Raman active, so that the SFG intensity includes contributions from the Raman polarizability as well as the IR selection mle for the normal mode. 

An extreme case of chemisorption-induced restructuring of metal surfaces is coirosive chemisorption as observed by SFG. In this circumstance, metal atoms break away from step or kink surface sites and form bonds with several adsorbate molecules. Carbon monoxide can form several carbonyl ligand bonds with platinum atoms leading to the creation of metal-carbonyl species. Thus, metal-metal bonds are broken in favor of forming metal-carbonyl clusters that are more stable at high CO pressures. The SFG vibrational spectra detect the reversible formation of new adsorb carbon monoxide species above 1(X) Torr on Pt(l 11), that appear to be platinum-carbonyl clusters Pt (CO) , with (m/n) > 1 and a CO commensurate overlayer. 

VEELS SFG vibrational electron energy-loss spectroscopy Sum-frequency generation Yes l° 212-218 No... 

SFG is a second-order non-linear optical process in which two laser beams overlap in a medium and generate the sum-frequency. As a second order process it is allowed on surfaces or interfaces, where the inversion symmetry is broken. In a typical experiment, one beam of infrared and the other of visible wavelength are mixed allowing SFG vibrational spectroscopy. 

York, R.L., Mermut, O., Phillips, D.C., McCrea, K.R., Ward, R.S., Somoijai, G.A. Influence of ionic strength on the adsorption of a model peptide on hydrophilic silica and hydrophobic polystyrene surfaces insight from SFG vibrational spectroscopy. J. Phys. Chem. C 111, 8866-8871 (2007)... 

One important use of SFG vibrational spectroscopy is the orientational analysis of ionic liquids at gas-liquid interfaces. For example, the study of the structural orientation ofionic liquids using common cation types, that is, [BMIM], combined with different anions, gives information on the effects of both cation and anion types [3, 22, 26-28]. Additional surface analytical work includes SFG studies under vacuum conditions for probing the second-order susceptibility tensor that depends on the polar orientation of the molecule and can be correlated to the measured SFG signal intensities. Supporting information is frequently obtained by complementary bulk spectroscopic techniques, such as Raman and Fourier transform infrared (FTIR) analysis, for the analysis of the pure ionic liquids. 

As briefly reviewed in this section, SFG vibrational technique has significant advantages to the conventional vibrational spectroscopy. A great deal of new information on the interfacial molecular structure will be elucidated by this method, which is important and useful for understanding and controlling the surface property and fimctionality of materials. Appearance of the new techniques such as SFG imaging as well as FT-SFG will make this method more powerful and more easy to use. It is also expected that more theoretical studies will be carried out to quantitatively understand all the information we can get from SFG measurements and to anticipate what we can further obtain from this method. 

A further insight toward the understanding of surfactant monolayers at SL interfaces can be found in the work by Miranda et al., where the authors used SFG vibrational spectroscopy to study the effect of the liquid environment on the chain conformation (Figure 11). ... 

Since the 1980s, the surface science community has developed techniques that probe the structure, composition, mechanical properties, and dynamics of surfaces at high pressure. The research activity on in situ surface characterization will be covered in Part 111. Several examples of high-pressure surface apparatuses are shown in Eig. 1.8. These include (a) high-pressure SFG vibration spectroscopy, (b) high-pressure STM, (c) high-pressure XPS, and (d) atomic force microscopy (AFM). 

Chen C, Wang J, Woodcock SE, Chen Z. Surface morphology and molecular chemical structure of poly(n-butyl methacrylate)/polystyrene blend studied by atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy. Langmuir 2002 18 1302-9. 

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