Elements line spectrum

There are three modes of analysis commonly used spectrum acquisition spatial distribution, or dot, mapping of the elements and elemental line scans. 

Since an atom of a given element gives rise to a definite, characteristic line spectrum, it follows that there are different excitation states associated with different elements. The consequent emission spectra involve not only transitions from excited states to the ground state, e.g. E3 to E0, E2 to E0 (indicated by the full lines in Fig. 21.2), but also transisions such as E3 to E2, E3 to 1( etc. (indicated by the broken lines). Thus it follows that the emission spectrum of a given element may be quite complex. In theory it is also possible for absorption of radiation by already excited states to occur, e.g. E, to 2, E2 to E3, etc., but in practice the ratio of excited to ground state atoms is extremely small,... 

It is important to note that we have tried to avoid carbon-rich stars, because they have a rich molecular line spectrum, mostly CN, CH and C2, obliterating many interesting atomic lines of rare elements. This is why we had in our sample a star, CS 31082-001, in which we were able to measure the 385.97 nm line of U II, whereas in the similar r-process element enriched star CS 22892-052, but carbon rich, a CN line obliterates the U II line. 

Compared to flame excitation, random fluctuations in the intensity of emitted radiation from samples excited by arc and spark discharges are considerable. For this reason instantaneous measurements are not sufficiently reliable for analytical purposes and it is necessary to measure integrated intensities over periods of up to several minutes. Modern instruments will be computer controlled and fitted with VDUs. Computer-based data handling will enable qualitative analysis by sequential examination of the spectrum for elemental lines. Peak integration may be used for quantitative analysis and peak overlay routines for comparisons with standard spectra, detection of interferences and their correction (Figure 8.4). Alternatively an instrument fitted with a poly-chromator and which has a number of fixed channels (ca. 30) enables simultaneous measurements to be made. Such instruments are called direct reading spectrometers. 

Qualitative analysis may be made by searching the emission spectrum for characteristic elemental lines. With modem high resolution optics and computer control, the emission spectrum may be readily examined for the characteristic lines of a wide range of elements (Figure 8.13). Quantitative measurements are made on the basis of line intensities which are related to the various factors expressed in equation (8.1). Under constant excitation... 

In addition to the check in the value of duo this spectrum shows (1) that the characteristic iodine reflections are more intense than the tungsten lines and (2) that, whereas the a-peak is always higher than the /8-peak for the regular reflected target line spectrum, the reverse is true for radiation characteristic of elements in the crystal. In all such cases so far in vestigated the a-peak is always smaller than the /8. 

There is more than one spectral line in the line spectrum of an element and therefore more than one line to choose from when setting the monochromator. For each element, there is one line that gives the optimum absorptivity for that element, and this line is therefore the most sensitive and useful. This line... 

Many hollow cathode lamps are needed because each element, since it must be contained in the cathode, requires a different lamp. Some lamps, however, are multielement. The element analyzed must be contained in the cathode so that its line spectrum will be generated and absorbed by the same in the flame. 

The primary line is the line in the line spectrum that is used most often for analyzing for that element because it is the most sensitive and useful. Secondary lines are other lines that are sometimes used for various reasons. 

Le Chatelier s principle Le ChOtelier s principle states that if a chemical system at equilibrium is stressed (disturbed), it will reestablish equilibrium by shifting of the reactions involved, limiting reactant The limiting reactant is the reactant that is used up first in a chemical reaction, line spectrum A line spectrum is a series of fine lines of colors representing wavelengths of photons that are characteristic of a particular element, liquid A liquid is a state of matter that has a definite volume but no definite shape, macromolecules Macromolecules are extremely large molecules. 

Present M sbauer Studies of Natural Pyroxenes and Olivines. Table IX gives the major element chemical compositions of the silicate minerals examined in this study. Table X compares the Mossbauer parameters of these minerals, while Figures 9-13 show representative Mossbauer spectra. Fayalite (Figure 9) is the only olivine in this group. The two lines are, however, somewhat broadened (0.35 and 0.39 mm./ sec.) compared with the width of natural iron foil lines observed with our source (0.24 mm./sec.) and suggest the near coincidence of two quadrupole-split doublets resulting from Mi and M2 sites. Analysis of this "two-line spectrum into a four-line spectrum in the manner described by Evans et al (11) could possibly yield parameters for the two iron sites, but this was not undertaken since both lines appear symmetric. The "two-line quadrupole splitting of 2.78 mm./sec. is somewhat smaller... 

Start 1D WIN-NMR, enter the Preview window and use the Frame option to open a frame for the 2D layout copied into the clipboard in the previous Check it. With the cursor positioned within the frame double click on the left mouse button to open the dialog box. Click on Paste and then OK to Import the 2D layout. Double click the left mouse button and in the Metafile Options dialog box adjust x-Factor and y-Factor to position the 2D layout correctly within the frame. Open additional frames to accommodate the entire 1D C spectrum D. NMRDATA GLUCOSE 1D C GC 001999.1 R) and the structural formula (Fig. 4.33). Arrange and resize these frames for the best representation. Use additional graphical elements (Lines, Rectangle) available within the Preview window of 1D WIN-NMR for assignment purposes. Set up your output device and plot the layout. 

X-ray fluorescence spectrometry (XRF) is a non-destructive method of elemental analysis. XRF is based on the principle that each element emits its own characteristic X-ray line spectrum. When an X-ray beam impinges on a target element, orbital electrons are ejected. The resulting vacancies or holes in the inner shells are filled by outer shell electrons. During this process, energy is released in the form of secondary X-rays known as fluorescence. The energy of the emitted X-ray photon is dependent upon the distribution of electrons in the excited atom. Since every element has a unique electron distribution, every element produces... 

The selection rules state that the total angular momentum quantum number may change by 1 or 0. Thus an element with several isotopes each with its own nuclear spin will present a line spectrum with a very complex and, under most experimental conditions, unresolved hyperfine structure. Nevertheless, as we shall see later, the overlap between the hyperfine components of a spectrum line is sufficiently incomplete to permit preferential excitation of one isotope in a mixture of isotopes by radiation from a lamp containing that same isotope. 

Phosphors doped with rare-earth elements show two types of CTL spectrum, namely emission from the excited species and recombination radiation, simultaneously. Figure 21 shows the CTL spectrum from the TL-phosphor BaS04 Eu in air containing ethanol vapor. The emission band with fine spectrum components at 420 nm is attributed to the excited HCHO. The line spectrum components peaking at 580 and 615 nm are attributed to the electronic transitions within Eu3+ ions. 

Modern atomic theory received a shot in the arm when it was recognized that the individual atom has light absorption and emission spectra occurring at narrow lines of the spectrum at specific wavelengths, as opposed to the broad bands typical of the polyatomic molecules and compounds. Since the line spectrum of each element is characteristic of that element, atomic spectroscopy can be used for precise elementary analysis of many types of chemically simple and complex materials. These studies make use of the wave character of light, as well as light s particle character. 

As explained in Chapter 1, section 7, unless a very high resolution monochromator, e.g. an echelle monochromator, is used to isolate a very narrow (< ca. 0.005 nm) band of light from a continuum spectrum prior to absorbance measurement, the sensitivity will be very poor.1,2 Although there are occasional reports of analysis by flame AAS using continuum sources such as xenon arc lamps, these are invariably from research laboratories. The vast majority of reported applications use single element line sources, and more than 99% of these applications use hollow cathode lamps. 

A hollow cathode lamp emits an intense line spectrum of the cathode element, of any other element present in the cathode, and of the filler gas (neon or argon). It is therefore necessary to be able to isolate the lines of the determinant element from any other emitted lines. If we do not, the difference between 7t and /0 will be greatly reduced, and the sensitivity unacceptably poor. Moreover, not all lines of the determinant element give equal sensitivity, and it is therefore also desirable to isolate the determinant line at the wavelength which gives the most useful sensitivity from all other lines. This is done with a grating monochromator. Figure 6 illustrates a typical optical layout in the monochromator of an atomic absorption spectrometer. 

Each element has its own line spectrum. This is why the line spectrum for an element is also considered to be a fingerprint for that particular element. Because the amounts of light given off by the excited atoms were in fixed amounts, Bohr termed them quantized amounts of light. These fixed amounts of energy proved that the electrons could only make certain jumps between the orbits that were at fixed distances in the atom. Because of these fixed, circular orbits, Bohr s model of the atom is often referred to as the solar system model of the atom (see Figure 3.4). 

The general construction of an atomic absorption spectrometer, which need not be at all complicated, is shown schematically in Fig. 1. The most important components are the light source (A), which emits the characteristic narrow-line spectrum of the element of interest an absorption cell or atom reservoir in which the atoms of the sample to be analysed are formed by thermal molecular dissociation, most commonly by a flame (B) a monochromator (C) for the spectral dispersion of the light into its component wavelengths with an exit slit of variable width to permit selection and isolation of the analytical wavelength a photomultiplier detector (D) whose function it is to convert photons of light into an electrical signal which may be amplified (E) and eventually displayed to the operator on the instruments readout, (F). 

Qualitative analysis may be made by searching the emission spectrum for characteristic elemental lines. Photographic recording is not normally used, but with modern high resolution optics and computer control, the emission... 

The bombardment of a metal target with a beam of high-energy electrons produces X rays with a line spectrum characteristic of each element present. This is virtually independent of chemical combination or physical state and, for example, the Ko, hues from molybdenum appear at the same place whether the target is the oxide, sulfide or the element... 

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