Sulfide group vibrations

Note that in all the examples discussed so far, infrared spectroscopy gives its information on the catalyst in an indirect way, via hydroxyl groups on the support, or via the adsorption of probe molecules such as CO and NO. The reason why it is often difficult to measure the metal-oxide or metal-sulfide vibrations of the catalytically active phase in transmission infrared spectroscopy is that the frequencies are well below 1000 cm-1, where measurements are difficult because of absorption by the support. Infrared emission and Raman spectroscopy, discussed later on in this chapter, offer better opportunities in this respect. 

Infrared Spectrum and Group Theoretical Analysis of the Vibrational Modes of Carbonyl Sulfide 160... 

Electronic levels (T ) and vibrational-rotational constants of the observed states are from the optical study of Barrow et al. (J ) and the microwave work of Tiemann et al. (2). Other low-lying electronic states and their vibrational-rotational constants are estimated in isoconfIgurational groups by analogy with BaO (8) and from trends observed in the known states of the other alkaline-earth oxides and sulfides. Thermodynamic functions are calculated using first-order anharmonlc corrections to and in the partition function Q = exp(-c ej /T). Uncertainty in the energy and molecular constants for the... 

Barrow (3). Other low-lying electronic states and their vibrational-rotational constants are estimated In IsoconfIguratlonal groups by analogy with CaO (4) and from trends observed In the known states of the other alkaline-earth oxides and sulfides (4). 

In this chapter we describe some applications of inelastic neutron scattering in surface chemistry, more particularly in studies of catalysts and adsorbed species [1]. Our emphasis will be on the spectroscopy. The subject matter is arranged broadly according to the type of catalyst metals ( 7.3), oxides ( 7.4), zeolites and microporous materials ( 7.5) and sulfides ( 7.6) and, within each group, according to the reactant molecules. We start ( 7.1) with a general discussion of surface vibrations. 

Ziolek and Decyk [935] decomposed ethanethiol and diethyl sulfide over hydrogen and alkali forms of X, Y, and ZSM-5 zeolites, and attempted to identify the sites of the zeolites being active in these reactions and, also, to elucidate individual reaction steps with the help of IR spectroscopy. After ethanethiol adsorption on Na-Y or M, Na-Y (M=Cs, K, Li), bands at 2980,2930,2915 and 2850 cm were observed due to C-H stretching vibrations, the intensity of which paralleled the catalytic activity. Depending on the various possible reaction pathways, either Br0nsted-acid OH groups or alkali metal cations were viewed as the catalytically active centers. 

The correlation, vibrational and relativistic effects to L NLO properties have been studied by selecting as model systems the Group Ilb sulfides ZnS, CdS and HgS [15]. These weakly bound systems are expected to have quite large vibrational (hyper) polarizabilities. To the best of our knowledge this was the first study which included the computation of all three contributions to the (hyper) polarizabilities. 

Figure 41 shows characteristic group frequencies of sulfides and disulfides. The stretching vibration of C-S bonds gives rise to a weak infrared but a strong Raman signal at 730-570 cm . Similarly, the S-S stretching vibration at 500 cm is a very strong Raman line but very weak infrared band (Fig. 42), Both Raman signals are very diagnostic in the conformational analysis of disulfide bridges in proteins.

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