Infrared absorption spectra system

The z-phase in a chromium-vanadium system was quite different from CrV04 with respect to the x-ray diffraction pattern, ESR absorption spectrum, and infrared absorption spectrum and could be reduced with ammonia at 400°C., thus differing from CrV04. Taking into account the infrared absorption spectra of a chromium-vanadium system, the... 

An interesting point is that infrared absorptions that are symmetry-forbidden and hence that do not appear in the spectrum of the gaseous molecule may appear when that molecule is adsorbed. Thus Sheppard and Yates [74] found that normally forbidden bands could be detected in the case of methane and hydrogen adsorbed on glass this meant that there was a decrease in molecular symmetry. In the case of the methane, it appeared from the band shapes that some reduction in rotational degrees of freedom had occurred. Figure XVII-16 shows the IR spectrum for a physisorbed H2 system, and Refs. 69 and 75 give the IR spectra for adsorbed N2 (on Ni) and O2 (in a zeolite), respectively. 

Ionic polysulfides dissolve in DMF, DMSO, and HMPA to give air-sensitive colored solutions. Chivers and Drummond [88] were the first to identify the blue 83 radical anion as the species responsible for the characteristic absorption at 620 nm of solutions of alkali polysulfides in HMPA and similar systems while numerous previous authors had proposed other anions or even neutral sulfur molecules (for a survey of these publications, see [88]). The blue radical anion is evidently formed by reactions according to Eqs. (5)-(8) since the composition of the dissolved sodium polysulfide could be varied between Na2S3 and NaaS with little impact on the visible absorption spectrum. On cooling the color of these solutions changes via green to yellow due to dimerization of the radicals which have been detected by magnetic measurements, ESR, UV-Vis, infrared and resonance Raman spectra [84, 86, 88, 89] see later. 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The absorption bands in the ultraviolet and visible part of the spectrum correspond to changes in the energy of the electrons but simultaneously in the vibrational and rotational energy of the molecule. In this way a system of bands is produced in the gaseous state. In the liquid state there is nothing of the rotational fine structure to be seen, and usually little or nothing of the vibrational structure, as a result of the interaction with the molecules of the solvent. With aromatic compounds in non-polar solvents such as hexane and carbon tetrachloride the vibrational structure is, however, still clearly visible in the ultraviolet absorption spectrum. This vibrational structure is mainly determined by the vibrations of the excited state, which therefore do not occur in the infrared and Raman spectrum of the normal molecule. 

O-protonation of 5,5-dimethyI-3-(N-pyrrolidyl)-2-cyclohexene-l-one [246], based on the infrared spectrum of its perchlorate (Leonard and Adamcik, 1959), was confirmed by ultraviolet spectra (Alt and Speziale, 1965). The protonation of the bicyclic system [247], which is certainly N-protonated owing to steric hindrance to meso-merism, leads to a cation with a maximum absorption at 212 nm (in ethanolic hydrochloric acid) and three strong infrared absorptions in the solid hydrochloride at 1655 cm-1 and 1720 cm 1 for the double bonds and at 2430 cm 1 for the NH-vibrations (Dolby et al., 1971). 

Badger and Yost (4) observed the infrared bands of IBr and classified them as the A 1I2-X S transition. They have shown that the dissociation products of the upper state are normal atoms. Brown (5) assigned a faint set of bands in the red as the B IIq X f system. By means of a vibrational analysis he found that the absorption spectrum of IBr is analogous to that of ICl. The... 

Zeolites. The weak Raman signals arising from the aluminosilicate zeolite framework allow for the detection of vibrational bands of adsorbates, especially below 1200 cm which are not readily accessible to infrared absorption techniques. Raman spectroscopy is an extremely effective characterization method when two or more colored species coexist on the surface, since the spectrum of one of the species may be enhanced selectively by a careful choice of the exciting line. A wide range of adsorbate/zeolite systems have been examined by Raman spectroscopy and include SO2, NO2, acety-lene/polyacetylene, dimethylacetylene, benzene, pyridine, pyrazine, cyclopropane, and halogens. Extensive discussions of these absorbate/zeolite studies are found in a review article by Bartlett and Cooney. ... 

One of the important functions of this infrared microscope is the measurement of the IR spectrum from a spatial region smaller than the diffraction limit. This possibility is already illustrated in Figure 29.4e. The TFD-IR spectrum, that corresponds to the IR absorption spectrum, was measured from a fluorescence region smaller than the IR diffraction limit. Infrared spectroscopy in a sub-micron region will be possible by using a high NA objective lens with the confocal optical system. 

In discussing infrared absorption spectra, we refer, first of all, to the papers by Dows and Schettino (54) and of Schettino and Salvi (55). Dows and Schettino (54) investigated the CO2 crystal spectrum in the frequency region corresponding to the combination tone of the intramolecular vibrations v and 1/3 u /y3 Ri 3720 cm-1). Schettino and Salvi (55) measured the infrared (IR) spectra of N2O and OCS crystals. The CO2 and N2O molecules are linear, have no permanent dipole moments, and form a simple cubic lattice upon crystallization. This lattice has four molecules per unit cell, which are oriented along the axes of a tetrahedron. The OCS molecule is also linear, but it forms a crystal of the trigonal system with one molecule per unit cell. 

Figure 2c shows the near-infrared luminescence spectrum of [Gd(hfac)3NIT-BzImH] compared to its lowest-energy absorption band system. At 5 K, both spectra show well-resolved structure that is similar to the patterns observed for the uncoordinated radical, as summarized in Tables 1 and 2. The corresponding electronic transitions can be observed for many other complexes of lanthanide or d-block metal ions with radical ligands [24-27, 30]. In general, the spectra for lanthanide complexes are very similar to those of the uncoordinated radicals. 

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