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Characteristic State Line

It can be assumed a priori [11] that the reason for the variable composition of the octachloroditechnetates may be either a variable oxidation state of technetium or substitution of some of the cations by H30+ ions. The first explanation was proposed [22], when the accuracy ( + 0.017 A) of the X-ray diffraction study by a photomethod [81] precluded the determination of the fine difference between the Tc-Tc distances in the [Tc2CI8]3- and [Tc2Cl8]2- anions, which is 0.03 A according to the latest X-ray diffraction data [11,35,60,63,82] (Table 1). An attempt was made [11] to determine the H30+ ions in potassium octachloroditechnetate, which led to their detection from the weak characteristic absorption lines in the infrared spectra (v OH) = 2965,2930, and 2865 cm-1 <5(HOH) = 1610 cm-1 [83,84]). The results [11] did not conflict with the revised X-ray diffraction data [82] according to which the K+ ions in the unit cell of potassium octachloroditechnetate (+ 2.5) are present in two non-equivalent positions sixfold (K ) and threefold (K") under these conditions, the sixfold positions were fully occupied by K+ ions, while the threefold positions were half-occupied. [Pg.196]

The most extensively studied stable cyclic cation radicals of the p-block elements are the seven 71-electron systems [E3N2]. The all-sulfur (E = S) and the all-selenium (E = Se) cations have been structurally characterised as dimers in the solid state (see 4.11 in Section 4.2.2).In solution, the monomeric radicals, including all the possible mixed S-Se systems, have been identified by their characteristic five-line (1 2 3 2 1) EPR spectra with additional hyperfine coupling to Se for the selenium-containing radicals. [Pg.56]

Amide. — It has been pointed out before that europium behaves more or less like the alkaline earths and is closely related to strontium and barium. It is found to react with liquid ammonia at —78° C in much the same way as the alkali metals forming a characteristic deep blue solution. Eu(NH2)2 can be isolated [260] from the blue solution. Recent electron paramagnetic studies [261] of solutions of europium in liquid ammonia showed the presence of complex hyperfine lines arising from Eu2+ (8 7/2, g — 1.990 0.002) besides the characteristic single line of the solvated electron (g = 2.0014 0.0002) K The departure of the Eu2+ <7-value from the free electron value is explained as being due to spin-orbit coupling and a slight admixture (3.5%) of the 6P7/2 state. [Pg.117]

In principle, positronium can be observed through the emission of its characteristic spectral lines, which should be similar to hydrogen s except that the wavelengths of all corresponding lines are doubled. Positronium is also the ideal system in which the calculations of quantum electrodynamics can be compared with experimental results. Measurement of the fine-structure splitting of the positronium ground state has served as an important confirmation of the theory of quantum electrodynamics. [Pg.1359]

This type of active site is also known as a mixed-valence copper site. Similarly to the type 3 site, it contains a dinuclear copper core, but both copper ions have a formal oxidation state of +1.5 in the oxidized form. This site exhibits a characteristic seven-line pattern in the EPR spectra and is purple colored. Both copper ions have a tetrahedral geometry and are bridged by two sulfur atoms of two cysteinyl residues. Each copper ion is also coordinated by a nitrogen atom from a histidine residue. The function of this site is long-range electron transfer, and it can be found, for example, in cytochrome c oxidase [12-14], and nitrous oxide reductase (Figure 5.1 e). [Pg.104]

While the stoichiometries of the Mn SOD enzymes appear to vary, the properties of the Mn-binding site do not. This is borne out in the electronic spectra of these proteins, which display a great degree of similarity despite the diversity of sources from which they have been isolated (Table II). This type of spectrum is distinctive for manganese in the trivalent oxidation state (3). The native enzymes are EPR silent, as might be anticipated if they contained Mn solely as the trivalent ion (S = 2) (1, 6,12,18-20, 24). However, when the enzymes are denatured, the characteristic six-line pattern of Mn(II) (I = 5/2) appears. Magnetic susceptibility studies with the E. coli SOD were consistent with the presence of a monomeric Mn(III) complex with a zero-field splitting of 1 to 2 cm-1 (4). The enzymes are additionally metal specific (however, see Refs. 36 and 37) metal reconstitution studies with E. coli and B. stearothermophilus revealed a strict requirement for Mn for superoxide dismutase activity (2, 22, 23). [Pg.199]

Althongh the S3N2+ radical cation (13) has been well characterized in solntion by its characteristic five-line (1 2 3 2 1) ESR signal (g = 2.01 an = 3.15G), this S-N heterocycle is nsnally fonnd in the solid state as the dimeric cation SeN4 + (7), in which two Vtt-electron S3N2+ rings are associated via weak intermolecnlar S-S interactions [d(S-S) = 300-310pm],... [Pg.4651]

Figure 1-11 shows clearly how the wavelengths of characteristic emission lines can be calculated, since the difference in energy between two states will equal h, where v is the frequency of the radiation emitted when the atom goes from one state to the other. Consider the Ka.i characteristic line, for example. The L level of an atom is actually a group of three closely spaced levels (Lj, Ln, and L, ), and the emission of the Kot line is due to a AT -> L, transition. The frequency of this line is therefore given by the equations... [Pg.18]

The Rotary Disk Electrode (RDE) - ASTM D6595 The RDE instrument has this name because the sample fluid is transported into a high temperature arc by means of a rotary carbon disc. The disc is immersed into the sample vessel, usually the bottle cover, and picks up oil and wear metals as it turns. The arc raises the energy states of the metal atoms in the oil causing them to emit their characteristic emission lines. [Pg.482]

Since mercury is present already in the atomic state in the cold vapor technique, there is no need for an atomiser as such. The sample vapor is swept directly from the reduction cell or the amalgamation trap in the carrier gas stream to a 10 cm length T-shaped quartz tube that is moderately heated (to ca. 200 °C to prevent condensation of mercury). This quartz cell is located in the light path of a conventional AA spectrometer where the attenuation of a characteristic Hg line source is measured. Dedicated AA spectrometers (which, in this case, often have a continuum light source) may also be used with longer absorption cells (300 mm pathlength) to increase the sensitivity. [Pg.452]

The practice of analytical spectroscopy preceded the development of the theories concerning the origin of spectra by a number of years. Bunsen and Kirchhoff studied spectra produced by salts and salt solutions heated in flames and noted the characteristic spectral line emissions of a number of elements. They also observed that substances absorb energy most strongly at the same wavelengths at which emission occurs. Their results led Kirchhoff to state that the power of emission is equal to the power of absorption for all... [Pg.14]

Following the adventurous story of terbium it is actually impossible to decide by now who was the true discoverer, Mosander, Delafontaine or Smith The element names, as indicated above were applied inconsistently, and we cannot know whether they referred to the same substance. Did Mosander find the same substance and called it erbium that finally became terbium with Delafontaine, or was Bunsen correct and consequently Mosander s fraction was a mixture only No data were reported that would allow us to state now, at this late date, what substances were identical, no characteristic spectral lines, no exact atomic weight values are at our disposal as yet. [Pg.51]

Since shortly after its inception in 1955, AAS has been the standard tool employed by analysts for the determination of trace levels of metals. In this technique a fine spray of the analyte is passed into a suitable flame, frequently oxygen-acetylene or nitrous oxide-acetylene, which converts the elements to an atomic vapour. Through this vapour is passed radiation at the right wavelength to excite the ground state atoms to the first excited electronic level. The amount of radiation absorbed can then be measured and directly related to the atom concentration a hollow cathode lamp is used to emit light with the characteristic narrow line spectrum of the analyte element. The detection system consists of a monochromator (to reject other lines produced by the lamp and background flame radiation) and a photomultiplier. Another key feature of the technique involves... [Pg.7]

The composition UO2.25 usually shows a fairly sharp diffraction pattern. The compound may show an ordered state if it has been carefully annealed. Three forms of U4O9 have been reported by Masaki, Masaki and Doi and Naito," all of which are cubic and based on a superstructure of the uraninite cell. None of these ordered compounds has been reported in natural samples. Although UO2.25 has been reported, the required annealing has evidently not occurred. Careful studies on natural samples may reveal the weak characteristic ordering lines. The phase should exist in natural systems. [Pg.46]

Figure 6b (bottom) reproduces the Mm (3p3/2- 5d) spectrum of y-Ce. As the Lm spectrum (top) the Mm absorption exhibits the characteristic absorption line of lanthanide p - d transitions. In Mm absorption Coster-Kronig transitions strongly increase the total lifetime broadening of the final states. Therefore mixed valent states can be only qualitatively traced from M, spectra (Kaindl et al. 1984). [Pg.471]


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See also in sourсe #XX -- [ Pg.86 ]




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