Spectral lines metal ions

Chapter 5 will show in more detail how the spectral width of optical transitions of active centers (particnlarly for transition metal ions) is affected by lattice vibrations. For the purpose of this section, we will just mention that these transitions are associated with the outer electrons of the active center (the 3d valence electrons), which show strong interactions with the phonons of the matrix in which they are embedded. As a result, the optical transitions, and particularly the emission lines, are strongly modulated by lattice vibrations. 

Spectral interferences. These interferences result from the inability of an instrument to separate a spectral line emitted by a specific analyte from light emitted by other neutral atoms or ions. These interferences are particularly serious in ICP-OES where atomic spectra are complex because of the high temperatures of the ICP. Complex spectra are most troublesome when produced by the major constituents of a sample. This is because spectral lines from other analytes tend to be overlapped by lines from the major elements. Examples of elements that produce complex line spectra are Fe, Ti, Mn, U, the lanthanides and noble metals. To some extent, spectral complexity can be overcome by the use of high-resolution spectrometers. However, in some cases the only choice is to select alternative spectral lines from the analyte or use correction procedures. 

Argon plasmas are used in optical emission spectrometry to atomise and ionise elements leading to the emission of characteristic spectral lines. Hence, a plasma torch (7-8 000 K) can be used for ionisation in mass spectrometry. Ions produced in the plasma are introduced into the mass analyser through a small orifice (called a skimmer) placed in the axial direction. Because the mass spectrometer is operated under a vacuum, the ions are sucked into the mass analyser through the skimmer. An aqueous solution of the sample can be aspirated into the plasma or, alternatively, the plasma can be placed at the exit of a gas chromatograph (e.g. speciation of organo-metallic compounds by GC/ICP-MS). Since all chemical bonds are broken in the plasma, the only accessible information is that concerning the concentration of monoatomic ions (Fig. 16.19). 

EPR systems. For organic radicals in solution, the homogeneity of the field should be better than about 0.005 mT over the sample region. The homogeneity requirements are not as severe for transition metal ions, due to their broader spectral lines. 

It seems that cases of strong coupling can be found in e.g. 3 d-TM s and probably also in 3 d-TM compounds and in many adsorbate systems. In such cases, the overlap between the localized orbital and the valence orbitals is quite large. The screening process then rather corresponds to a pronounced shift of the bonding charge towards the central metal ion or towards the adsorbate, and the lowest line picks up most spectral strength and also becomes the main line. 

The spectral lines of the Fe atom and ions are very prominent in the spectra of stars. For this reason, coupled with its high abundance, iron has been a standard measure ofthe abundance ofheavy elements within stars. Often the ratio Fe/H, the ratio of the abundance ofiron to that of hydrogen, is taken as a measure of the metallicity of the star. It provided one of the earliestand best indications thatvery old stars within... 

The strengths of the spectral lines of the cobaltatom and ion are measurable in composite spectra from stars, where iron is also observable and is usually taken as a standard measure of the abundance of heavy elements within stars. Observations show that the abundance ratio Co/Fe has, through most of galactic history, remained constant, even while each has increased in its proportion to H. A puzzle exists only in the most metal-poor stars, where stunning recent observations reveal a Co/Fe ratio that is almost five times greater than solar when Fe/H is near 1/10 oooth of that in the Sun, and that ratio... 

In general, lanthanide atoms or ions with an unfilled 4f shell have about 30 000 visible spectral lines. Transition metals with an unfilled 5d shell have about 7000 visible spectral lines. Main group elements with an unfilled p shell only have about 1000 visible spectral lines. Lanthanide elements, therefore, have more electronic energy levels and spectral lines than the more common elements. They can absorb electromagnetic waves from the ultraviolet to the infrared and emit their characteristic spectra. 

A light-induced ESR signal of P-682 resembling that of P-700 has been detected at cryogenic temperatures [74,75] its spectral characteristics (g = 2.002 and line-width of 6-8 G) are similar to those observed for a ligated chlorophyll a cation radical in aprotic solvents [76]. It is unclear, therefore, if P-682 is a dimeric structure or a single chlorophyll a molecule ligated to a metal ion (see Fig. 4.4). 

The negative ion of naphthalene can be made in a suitable solvent, such as di-methoxyethane (dme), by treatment with an alkali metal in the absence of oxygen. This stable free radical-ion has an esr spectrum with hyperfine structure. If more naphthalene is added, a broadening of the spectral lines occurs which is attributed to the reaction... 

The first dye used in an electrophosphorescent LED was the terbium-complex Tb(acetyhlacetonate)3 (Tb(acac)3, see Fig. 11.2) [21], LEDs based on complexes with rare-earth central metals such as terbium or europium are very interesting for display applications, because they emit light with a very small spectral line width. These sharp emission lines are due to f-f transitions located on the central metal ion. Disadvantages of these complexes are, however, that color tuning via the chemical modification of the ligand is not possible and that the radiative lifetime of phosphorescence is rather long. 

Another problem under current investigation by high resolution 13C nmr is the interaction between and association of nucleotides and proteins. Line broadening effects and changes in the chemical shifts in the 1 3 C spectrum of ATP similar to the spectral changes noted for nucleotide metal ion complexation, were observed upon the addition of ferrocytochrome (Kayushin and Ajipa, 1973). 

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