Spectral line identifications

The characteristic lines observed in the absorption (and emission) spectra of nearly isolated atoms and ions due to transitions between quantum levels are extremely sharp. As a result, their wavelengths (photon energies) can be determined with great accuracy. The lines are characteristic of a particular atom or ion and can be used for identification purposes. Molecular spectra, while usually less sharp than atomic spectra, are also relatively sharp. Positions of spectral lines can be determined with sufficient accuracy to verify the electronic structure of the molecules. 

X-ray fluorescence analysis is a nondestructive method to analyze rubber materials qualitatively and quantitatively. It is used for the identification as well as for the determination of the concentration of all elements from fluorine through the remainder of the periodic table in their various combinations. X-rays of high intensity irradiate the solid, powder, or liquid specimen. Hence, the elements in the specimen emit X-ray fluorescence radiation of wavelengths characteristic to each element. By reflection from an analyzing crystal, this radiation is dispersed into characteristic spectral lines. The position and intensity of these lines are measured. 

Ca brick-red, Sr carmine-red, etc). If a flame can be kept burning uniformly for an extended period of time and material fed into the flame at a const rate, the intensity of the spectral line or band will be a measure of the concn of the substance. The wave length of the emitted light will permit identification of the excited species... 

Depending on conditions, frozen substances in comet nuclei can be crystalline ices, amorphous ices, and clathrate hydrates (compounds in which cages in the water-ice lattice can host guest molecules). Compositions of the ices and associated organic materials in comets have been determined from both telescopic and spacecraft observations. Spectral line measurements of gases in a comet s coma allow the identification of molecules and radicals. An inherent difficulty in spectral measurements is that volatiles in the coma are commonly broken... 

The optical emission spectrum of uranium, while exceedingly rich in lines, cannot be depended upon in the detection and identification of this element. None of its lines is sufficiently persistent, and unless a comparatively large quantity of uranium is present in the zone of excitation, no spectral lines will be observed. On the other hand, it is possible to make use of a simple photoluminescence reaction which will enable the chemist to detect small traces of uranium. 

These can be performed successfully with AES. Indeed, the unambiguous detection and identification of a single non-interfered atomic spectral line of an element is sufficient to testify to its presence in the radiation source and in the sample. The most intensive line under a set of given working conditions is known as the most sensitive line. These elemental lines are situated for the various elements in widely different spectral ranges and may differ from one radiation source to another, as a result of the excitation and ionization processes. Here the temperatures of the radiation sources are relevant, as the atom and ion lines of which the norm temperatures (see Section 1.4) are closest to the plasma temperatures will be the predominant ones. However, not only will the plasma temperatures but also the analyte dilutions will be important, so as to identify the most intensive spectral lines for a radiation source. Also the freedom from spectral interferences is important. 

I have sketched a small portion of the gas-phase chemistry that produces the observable species. The extremely high quality factor of the radioastronomical observed spectral lines coupled with the large munber of observable transitions for each species has resulted in unambiguous identification of more than one hundred molecular species. In further confirmation, isotopic variants, designated isotopomers for lack of a better word, are foimd for virtually every relatively abundant species. The observations and species listed are within the galaxy and do not give the isotopomers. That this chemistry is universal is shown by the extensive list of molecules observed in other galaxies (Table 17.5) (Bertoldi et al., 2003). 

Assignment to residue type is accomplished readily by systematic spin decoupling, since the spectrum of each amino acid has a characteristic coupling pattern. This is illustrated in Figure 23, where the decoupled residue is identified readily as tyrosine by comparing the decoupling pattern to the spectrum of this amino acid [67]. The only requirement for the success of this procedure is extensive resolution of spectral lines and line widths sufficiently narrow to permit the identification of multiplets. 

The usefulness of 2DFT techniques is especially great in systems of coupled spins, whether the coupling is by dipolar or scalar interactions, chemical exchange or cross-relaxation. The evolution of such coupled systems after an initial perturbation can be predicted theoretically and pulse sequences can be designed on the basis of the theoretical analysis which will generate additional spectral lines related in frequency to both coupled lines, thereby permitting an easy identification of the pairs of lines that correspond to each coupled system. 

The solute molecule is dissolved in the liquid crystal solvent at low concentration. A variety of nematic solvents are available, some of which are nematic at room temperature. Representative high-resolution proton NMR spectra are given in Figure 1. Because the solvent order depends on composition and temperature, it is important that temperature and composition gradients at the NMR probe be minimized if the narrow line widths of a few hertz are to be obtained. The spectra of Figure 1 show the rapid increase of spectral complexity with the number of nuclei. The spectra become almost continuous and uninterpretable at about 10 spins. Simplified proton NMR spectra can be obtained by partial deuterium substitution and decoupling.6 This has been described for cyclohexane, but has not been used extensively. Proton double resonance is also a useful experimental technique for the identification of spectral lines.6... 

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