Studies by Infrared Spectroscopy

Ultraviolet and visible absorption spectroscopy has been a powerful aid to studies of free radicals in the gas phase but is of less value in the solid phase because of line broadening and consequent lack of resolution. Under suitable conditions, however, solid state infrared spectra can give information on the structure of free radicals and on the forces holding the constituent atoms in their equilibrium positions. The technique is less sensitive than e.s.r. because the extinction coefficients of vibrational transitions are generally low but the ability to observe non-para-magnetic molecules in addition to free radicals is sometimes advantageous. 

The infrared spectrum of a deposit prepared with the rotating cryostat is recorded in situ (see Section IIF2) and so the deposit can be removed later and its e.s.r. spectrum recorded. This helps in the assignment of absorption bands to the free radical species as the changes that occur in the infrared spectrum when the sample is warmed can be related directly to the changes in the e.s.r. spectrum. 

The comparison of the spectra of stable molecules deposited on the drum of the cryostat with those obtained by normal transmission infrared spectroscopy show that the spectra observed from deposits on the drum are characteristic of transmission spectra rather than reflectance spectra. Since the matrices used have not been completely transparent blank runs have been necessary. 

The infrared spectrum of CO2 radical ion (prepared by depositing sodium atoms on solid carbon dioxide) has been obtained and has bands 

The structurally similar radical ion, CS, has also been examined. The thermal behaviour of a strong band at 1161 cm correlated very well with that of the e.s.r. spectrum and it is attributed to a fundamental vibration of CS. As e.s.r. studies (Bennett et al., 1967c) show that the radical ion is non-linear, this band is probably due to the anti-symmetric stretching mode of CS. When potassium, instead of sodium, was used to prepare the radical ion, the band shifted to 1180 cm , which indicates that there is a perturbation of the CS radical ion by the counter-ion. This is in agreement with the e.s.r. results which show that the gr-tensor is affected by the counter-ion. 

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Complexes. The structure of an n a charge-transfer complex between quinoxaline and two iodine atoms has been obtained by X-ray analysis and its thermal stability compared with those of related complexes. The hydrogen bond complex between quinoxaline and phenol has been studied by infrared spectroscopy and compared with many similar complexes. Adducts of quinoxaline with uranium salts and with a variety of copper(II) alkano-ates have been prepared, characterized, and studied with respect to IR spectra or magnetic properties, respectively. 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

This process has been studied by infrared spectroscopy by Dwyer (22), using 9% Pt/Si02 and the cell used by Ueno et al. (19). The bands arising from gaseous CO2 and surface CO were followed after a switch in the gas phase composition from 3kPa O2 in helium, to pure helium for a few seconds and then to 2kPa CO in helium. 

R. Ryberg, Carbon-Monoxide Adsorbed on Cu(100) Studied by Infrared-Spectroscopy, Surf. Sci. 114 (1982), 627 641. 

F. Freund, R.M. Knobel, Distribution of fluorine in hydroxyapatite studied by infrared spectroscopy, J. Chem. Soc. Dalton 11 (1977) 1136-1140. 

A large variety of problems related to the nature of the adsorption processes have been studied by infrared spectroscopy. The most extensive and productive application of this method has been in studies of chemisorption on supported-metal samples. Spectra of physically adsorbed molecules have provided important information on the interaction of these molecules with the surface of the adsorbent. Experimental developments have reached a state where it is evident that the infrared techniques are adaptable to practically all types of samples which are of interest to catalytic chemists. Not only are the infrared techniques applicable to studies of chemisorption and physical adsorption systems but they add depth and preciseness to the definitions of these terms. 

The sealed tube reaction of Bi203 with BiF3 at 670°C produces BiOF together with three phases having the composition BiIF3 2x Single crystals of BiOF have been studied by infrared spectroscopy (113). 

Solubilization of carboxylic acids, such as acetic acid and oleic acid, by dino-nylnaphtalenesulfonates (DNNS) in hexane was studied by infrared spectroscopy. Since DNNS salts form reverse micelles and have an aggregation number of approximately 7 in low polar solvents, carboxylic acids would be solubilized in the polar core of the RMs (Inoue and Nose, 1987 Inoue et al. 1965). 

The tautomerism between 2-pyridinethione and 2-pyridine thiol has also been examined using variable temperature IR spectroscopy <2002JOC9061>. No evidence for the S-H stretch was observed in a range of solvents and this was determined computationally to be a solvent effect the thiol form is more stable in the gas phase but the thione is more stable in solution. (The effect of phase on the tautomers of 2-hydroxy, 2-amino-, and 2-thiopyridine has also been studied by infrared spectroscopy <2001SAA2659>.) Dimerization is also observed, with the indication that the thione dimer predominates, in contrast with the computational studies described above. 

Szollosi, G. and Bartok, M. Role of basic and acidic centers of MgO and modified MgO in catalytic transfer hydrogenation of ketones studied by infrared spectroscopy, J. Mol. 

Thus, adsorption of NH3 on alumina resembles that of water in many respects. Both molecules are adsorbed molecularly at low temperatures but are chemisorbed dissociatively at higher temperatures. Ammonia is held strongly on A1203 surfaces and cannot be removed completely even on desorption at 500°C. Various species occur simultaneously, their relative importance being determined by the OH content of the surface. Furthermore, displacement adsorptions may take place. Thus, NH2" ions readily replaced chloride ions on surfaces of chlo-rided aluminas (166). One has, therefore, to conclude that ammonia retention on aluminas cannot be an acceptable measure of surface acidity and can hardly be related to catalytic activity. Ammonia adsorption on aluminas as studied by infrared spectroscopy, perhaps combined with TPD experiments (173), gives ample information on surface properties but ammonia cannot be used as a specific poison on alumina. 

Casal, H.L., Mantsch, H.H. 1984. Polymorphic phase behavior of phopholipid membranes studied by infrared spectroscopy. Biochim. Biophys. Acta 779, 382-401. 

The water-rock/soil and organic matter-minerals (including soil organic matter-clay), interactions can also be studied by infrared spectroscopy (Chapter 2, Section 2.1.2). 

Mantsch, H. H. and McElhaney, M. J. Phospholipid phase transitions in model and biological membranes as studied by infrared spectroscopy. Chemistry and Physics of Lipids 57(2-3) 2l3-226, 1991. 

Casal, H. L. and Mantsch, H. H. Polymorphic phase behavior of phospholipid membranes studied by infrared spectroscopy. Biochimica et Biophysica Acta 779 381-401, 1984. 

The structure of thietane 1-oxide has been investigated by microwave spectroscopy dihedral angle 145.1°, C-S, 1.836A C-C, 1.542A C-S-C 75.7°, C-C-C, 95.9° S-C-C, 89.6°. The sulfoxide oxygen prefers the equatorial position. The ring-puckering has also been studied by infrared spectroscopy the barrier to interconversion between a stable equatorial form and an axial conformer is about 3440 cal/mole. ... 

Oare earth forms of zeolites X and Y type faujasites possess superior catalytic properties for various reactions such as alkylation, isomerization, and cracking (9, 12, 18). Structural studies involving x-ray diffraction and CO chemisorption have been made to locate the positions of the rare earth (11, 14, 16). Hydroxyl groups and their relationship to surface acidity have been studied by infrared spectroscopy, utilizing the adsorption of pyridine and other basic molecules (2, 6, 21, 22, 23). Since much of the previous research has involved measurements on mixed rare earth faujasites, a need existed for a more systematic study of the individual rare earth zeolites, in regard to both structural and catalytic properties. The present investigation deals with the Y, La, Ce, Pr, Sm,... 

The azide-tetrazole equilibrium (equation 4) has been studied by infrared spectroscopy and settled in favour of the azide form. 

The electrochemical and infrared spectroscopic measurements have confirmed that the adsorbed CO is formed during CO reduction. However, it still remains ambiguous whether the adsorbed CO is a real intermediate species to produce hydrocarbons or stable poison species. Thus negative polarization of CO adsorbed on Ni electrode was studied by infrared spectroscopy at ambient temperature. 

Folman, M., Fastow, M., and Kozirovski. (1997). Surface heterogeneity of C g as studied by infrared spectroscopy of adsorbed CO and adsorption potential calculations. Langmuir, 13, 1118—22. 

I.A. Beta, H. BOhlig B. Hunger (2004). Phys. Chem. Chem. Phys., 6, 1975-1981. Structure of adsorption complexes of water in zeolites of different types studied by infrared spectroscopy and inelastic neutron scattering. 

The polymer structures were studied by infrared spectroscopy and NMR. Infrared is ineffective in distinguishing between polymers of these three types. In all three cases, C-H bonds signals are observed at 2950, 2920, and 1450 cm1, and a band at 1375 cm1 may be attributed to methyl groups. 

Infrared spectroscopy is used for the analysis of almost all the fractions and products of crude oil. However, in the last century, a very interesting purpose of the infrared spectroscopy has been developed. It is the dynamic monitoring of the changes in the structure of lubricating oils as it undergoes degradation. Many processes such as oxidation or polycondensation in oils can be studied by infrared spectroscopy. 

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