Inelastic vibrational spectroscopy

Vibrational spectroscopy provides detailed infonnation on both structure and dynamics of molecular species. Infrared (IR) and Raman spectroscopy are the most connnonly used methods, and will be covered in detail in this chapter. There exist other methods to obtain vibrational spectra, but those are somewhat more specialized and used less often. They are discussed in other chapters, and include inelastic neutron scattering (INS), helium atom scattering, electron energy loss spectroscopy (EELS), photoelectron spectroscopy, among others. 

Kearley, G. J., Pressman, H. A. Slade, R. C. T. (1986). The geometry of the HjOJ ion in dodecatungstophosphoric acid hexahydrate, (HjOJ)j (PWjjOfo), studied by inelastic neutron scattering vibrational spectroscopy. Journal of the Chemical Society Chemical Communications, 1801-2. 

Supplementary to other vibrational spectroscopies, inelastic neutron scattering (INS) spectroscopy is a very useful technique for studying organic molecules as it is extremely sensitive to the vibrations of hydrogen atoms. INS spectroscopy has been used to analyze the molecular dynamics of the energetic compound ANTA 5 <2005CPL(403)329>. 

Another technique of vibrational spectroscopy suited for the characterization of solids is that of Raman spectroscopy. In this methodology, the sample is irradiated with monochromatic laser radiation, and the inelastic scattering of the source energy is used to obtain a vibrational spectrum of the analyte [20]. Since... 

Mazur U, Hipps KW (2001) Inelastic electron tunneling spectroscopy. In Chalmers J, Griffiths P (eds) Handbook of vibrational spectroscopy, vol 1. Wiley, New York, pp 812-829... 

Inelastic electron tunneling spectroscopy (lETS) takes advantage of the general applicability of vibrational spectroscopy by measuring the vibrational spectrum of molecules adsorbed on the insulation of a metal-insulator-metal junction (Figure 1). 

Thus far the discussion has centered on elastic tunneling, but consideration of inelastic processes may offer additional analytical opportunities. An energy scale of the relevant phenomena is presented in Table 2. Inelastic tunneling was first observed in metal-oxide-metal junctions. It was immediately developed as a technique for photon-free vibrational spectroscopy (lETS) where the tunneling electrons dissipate energy by coupling to vibra-... 

The cross-section in Eq. (1 illustrates another distinguishing feature of inelastic neutron scattering for vibrational spectroscopy, i.e., the absence of dipole and polarizability selection rules. In contrast, it is believed that in optical and inelastic electron surface spectroscopies that a vibrating molecule must possess a net component of a static or induced dipole moment perpendicular to a metal surface in order for the vibrational transition to be observed ( 7,8). This is because dipole moment changes of the vibrating molecule parallel to the surface are canceled by an equal image moment induced in the metal. 

II. Vibrational Spectroscopy of Adsorbed Molecules by Inelastic Neutron Scattering... 

Although the question of orientation order does not arise, these results for argon monolayers illustrate several features of neutron vibrational spectroscopy. Well-defined excitations can be observed at somewhat lower energy transfers than accessible with optical and electron energy-loss spectroscopies. Typical energy resolution in the scans of Fig. 2 is 0.3 meV (2.4 cm"1). The capability of obtaining inelastic spectra at constant non-zero Q is also not present in these other spectroscopies. However, scattered intensities are relatively low. Counting times in Fig. 2 were -30 minutes per point. 

C. A model system for neutron vibrational spectroscopy of adsorbed molecules monolayer butane on graphite. In this section we concentrate on a particular system, monolayer n-butane adsorbed on graphite, for which a considerable effort has been made to analyze the inelastic neutron spectra for the orientation of the adsorbed molecule and the forces bonding it to the substrate (10,19,20). By treating one system in greater detail, we can better illustrate the capabilities and limitations of the technique. 

D. Inelastic neutron spectroscopy applied to molecules chemisorbed on catalytic substrates, tne model system considered in the previous section is of interest in demonstrating the degree to which neutron vibrational spectra can be interpreted on a well-characterized substrate. Unfortunately from the standpoint of this symposium, the graphite substrates in these experiments are not chemically active. Therefore, in this section, we wish to... 

Although not exhaustive, the above summary of experiments with hydrogen chemisorbed on transition-metals serves to illustrate how neutron vibrational spectroscopy is performed with catalytic substrates and the methods used to analyze the inelastic neutron spectra. In concluding this section we note that the technique can be extended to supported catalysts such as in recent experiments with hydrogen adsorbed on both MoS and alumina supported MoSp (38). Also, as another indication of the variety of systems which can be studied, we note earlier experiments with ethylene (39) and acetylene (40) adsorbed on silver exchanged 13X zeolites. "Tn this work, deuteration of the molecules was helpful in identifying the surface vibratory modes on these ionic substrates of greater complexity. 

FTIR spectroscopy is a class of vibrational spectroscopy similar to Raman spectroscopy which provides molecular-level information based on the absorption of electromagnetic radiation, rather than inelastic scattering in Raman. 

Keywords Vibrational spectroscopy scanning tunneling microscopy and spectroscopy conductance inelastic conductance single-molecule chemistry controlled manipulation mode-selective reactivity. 

Vibrational spectroscopy is based on two fundamental processes excitation and detection. As we shall see later in this chapter, they are not equivalent, and indeed both have to be treated to understand the origin of active modes in the spectra. The excitation is based on inelastic scattering processes, thus connecting initial and final states with different energy. The detection relies on the effect of the new inelastic channel on experimentally observable magnitudes, i.e. the junction conductance. 

In this section, we introduce the working principle of vibrational spectroscopy. It will be compared with a parent technique called Inelastic Electron Tunneling Spectroscopy, which was developed in the 60 s. Although the working principle is similar in each of them, the specific nature of electron-vibration interaction differs. We shall conclude this section by reviewing the most important achievements of single-molecule vibrational spectroscopy. 

Volume 50 of Advances in Catalysis, published in 2006, was the hrst of a set of three focused on physical characterization of solid catalysts in the functioning state. This volume is the second in the set. The hrst four chapters are devoted to vibrational spectroscopies, including Fourier transform infrared (Lamberti et al.), ultraviolet Raman (Stair), inelastic neutron scattering (Albers and Parker), and infrared-visible sum frequency generation and polarization-modulation infrared rehection absorption (Rupprechter). Additional chapters deal with electron paramagnetic resonance (EPR) (Bruckner) and Mossbauer spectroscopies (Millet) and oscillating microbalance catalytic reactors (Chen et al.). 

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