Vibrational analysis adsorbed molecules

Adsorbed CO layers, bonding and Interactions, 559-61 Adsorbed molecules, vibrational analysis, 392-V03 Adsorbed species and processes on surfaces, IR spectroscopic characterizations, VOV-19 Adsorption... 

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

Determination of surface functional groups, e.g., —OH, —C - C—, and >C = O, and identificadon of adsorbed molecules comes principally from comparison with vibrational spectra (infixed and Raman) of known molecules and compounds. Quick qualitative analysis is possible, e.g., stretching modes involving H appear for v(C—H) at 3000 cm and for v(0—H) at 3400 cm L In addition, the vibrational energy indicates the chemical state of the atoms involved, e.g., v(C=C) " 1500 cmT and v(C=0) " 1800 cm"L Further details concerning the structure of adsorbates... 

IBACH AND MCller Vibrational Analysis of Adsorbed Molecules... 

Adsorption of a specific probe molecule on a catalyst induces changes in the vibrational spectra of surface groups and the adsorbed molecules used to characterize the nature and strength of the basic sites. The analysis of IR spectra of surface species formed by adsorption of probe molecules (e.g., CO, CO2, SO2, pyrrole, chloroform, acetonitrile, alcohols, thiols, boric acid trimethyl ether, acetylenes, ammonia, and pyridine) was reviewed critically by Lavalley (50), who concluded that there is no universally suitable probe molecule for the characterization of basic sites. This limitation results because most of the probe molecules interact with surface sites to form strongly bound complexes, which can cause irreversible changes of the surface. In this section, we review work with some of the probe molecules that are commonly used for characterizing alkaline earth metal oxides. 

DRS has been applied both to the analysis of vibrational spectra of surface species in the fundamental, overtone, and combination band regions,and to the determination of time correlation motion of adsorbed molecules by Fourier inversion of the spectra onto... 

The Nph molecules adsorbed from a solution in hexane on the NaX zeolite surface exhibite a strong emission consisting of structured fluorescence and phosphorescence and an additional structureless band with a peak at 400 ntn (Fig.l). The vibrational analysis of the structural spectra is presented in Table 1. 

SERS) recorded. From the comparison of the SERS spectra of the photochromes with those of the indoline and chromene model molecules (Figure 9), it was established that the SERS spectra of SPP (4) and SPOX (3) are mainly dominated by the vibrational characteristics of the indolinic moiety. Moreover, the detailed assignment of the SERS data, performed on the basis of the vibrational analysis of the NIR-FT Raman spectra of the pure substances, has enabled deduction of the geometry of the adsorbed species,48 shown in Figure 10. 

Vibrational analysis has turned out to be an additional valuable tool for giving better insight into details of the changes of molecular properties upon interaction with the zeolite surface. In the case of polyatomics the bonds which are mainly affected by interaction, and to what extent, must be traced out. This is accomplished by comparing the force constants of the free and adsorbed molecules. Furthermore, information on the geometry of the sorption complex may be obtained. Normal coordinate analysis using a harmonic valence force field has been carried out for cyclopropane in faujasites and mordenites, propene in different zeolites A and Y and cis-and /ra/25-but-2-ene in zeolites A [58-61]. 

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