Spectroscopic studies high-pressure

Maybe the best resource for input parameters are original publications, because these provide not just the data per se but also the context in which they were obtained and often an estimate of their uncertainties. Obvious sources for input data are, for example, kinetic studies (high-pressure rate expressions) and spectroscopic measurements (molecular properties)... 

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

Vibrational spectroscopic studies of heterogeneously catalyzed reactions refer to experiments with low area metals in ultra high vacuum (UHV) as well as experiments with high area, supported metal oxides over wide ranges of pressure, temperature and composition [1]. There is clearly a need for this experimental diversity. UHV studies lead to a better understanding of the fundamental structure and chemistry of the surface-adsorbate system. Supported metals and metal oxides are utilized in a variety of reactions. Their study leads to a better understanding of the chemistry, kinetics and mechanisms in the reaction. Unfortunately, the most widely used technique for determining adsorbate molecular structure in UHV,... 

Phase transitions in 1,3,4-oxadiazole crystals under high pressure were studied by Orgzall et al. <1999MI1949, 2003MI1805>. Later, during Raman spectroscopic investigations of crystalline 2,5-di(4-nitrophenyl)-l,3,4-oxadiazole... 

Ford et al.60 also made a significant contribution to the metal carbonyl catalyzed shift reaction in acidic medium. A solution of Ru3(CO)i2 (0.006-0.024 M with 0.25-2.0 M H2S04 4.0-12.0 M H20) in 5 ml of diglyme had good catalytic activity at 100 °C. They used a batch reactor with Pqo = 0-9 atm. Typical H2 turnover activity was reported to be about 50 turnovers per day. Their in situ spectroscopic studies show that the principal component was HRu2(CO)8-. They found that, at low CO partial pressures (< 1 atm), the catalysis was first order in Ru. However, at high CO partial pressures, the rate was inhibited. On the basis of their studies, they proposed the catalytic cycle outlined in Scheme 15. 

In situ studies of catalytic reactions have also been a prime focus of our group. The high-pressure spectroscopic technique used in our research is polarization modulation IR reflection absorption spectroscopy (PM-IRAS). Like SFG, PM-IRAS is a highly surface-sensitive technique that yields vibrational information about adsorbed surface species. Unlike SFG, however, PM-IRAS... 

Y. K. Vohra, Spectroscopic studies on diamond anvil under extremes static stress, in Recent Trends in High Pressure Research, A. K. Singh, ed., Oxford and IBH Pubhshing Co., New Dehh, 1992. 

Haynes, A. (2005) The use of high pressure spectroscopy to study catalytic mechanism, in Mechanisms in Homogeneous Catalysis, A Spectroscopic Approach (ed. B. Heaton), Wiley-VCH Verlag GmbH, Weinheim, pp. 107-50. 

As described earlier, high pressure cells have been developed for the use of noble gases as solvents for IR spectroscopic studies, either at low temperature, or at ambient temperature where the supercritical phase exists. A particular focus of this work was the study of reactive complexes containing coordinated noble gas atoms or molecular H2, the latter being particularly relevant to hydrogenation reactions. 

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