Emission atom lines

The almost featureless spectrum at 1.0 MHz is reminiscent of the result by Matula et al. [35], i.e., the SBSL spectrum from NaCl solution indicated only continuum emission with no atomic lines. Sonoluminescing bubbles at higher frequencies are smaller and interact less with surrounding bubbles. These factors may explain why the MBSL spectrum at 1 MHz is similar to that of SBSL. 

Atomic line emissions from Ti in the UV and visible regions of the electromagnetic spectrum (see Figure 8.6). 

Atomic line emissions are produced by the excitation of atoms as discussed previously. The emission of the light occurs at positions in the spectrum corresponding to definite wavelengths or frequencies. 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

Experimental details for the cross-section measurements were presented in the literature. Briefly, after the irradiation by electron beam pulse for a few nanoseconds, the time-dependent absorption for the atomic line transition Rg Rg -i-/zv was measured to observe the time-dependent population of the excited rare gas atoms Rg. The population of excited Rg was determined using an absorption law for the atomic lines, where the broadening of the absorption profile due to the thermal Doppler effect and due to the attractive interatomic potentials was reasonably taken into consideration. The time-dependent optical emission from energy transfer products, such as ... 

Obviously, the clusters NaAry (c), NaAry (c), NaAr4 (c), NaAry (d), and NaAre (c), which correspond to the simple van der Waals long distance addition of a excited sodium atom to an argon cluster, are characterized by 3p states and 3s states only weakly shifted with respect to the isolated atom limit. Their emission lines are therefore very close to the atomic line. 

Of course, this exact overlap is no accident, as atomic absorption and atomic emission lines have the same wavelength. The very narrowness of atomic lines now becomes a positive advantage. The lines being so narrow, the chance of an accidental overlap of an atomic absorption line of one element with an atomic emission line of another is almost negligible. The uniqueness of overlaps in the Walsh method is often known as the lock and key effect and is responsible for the very high selectivity enjoyed by atomic absorption spectroscopy. 

Most elements are almost completely singly ionized in the argon ICP (a fact which also makes it an ideal ion source for mass spectrometry), hence the majority of the most sensitive emission lines result from atomic transition of ionised species, so-called ion lines, with fewer sensitive atom lines. Ion lines are usually quoted as, e.g., Mn II 257.610 nm and atom lines as, e.g., Cu 1324.754 nm, with the roman numerals II and I denoting ionic and atomic species, respectively. 

It is also possible to use an internal standard to correct for sample transport effects, instrumental drift and short-term noise, if a simultaneous multi-element detector is used. Simultaneous detection is necessary because the analyte and internal standard signals must be in-phase for effective correction. If a sequential instrument is used there will be a time lag between acquisition of the analyte signal and the internal standard signal, during which time short-term fluctuations in the signals will render the correction inaccurate, and could even lead to a degradation in precision. The element used as the internal standard should have similar chemical behaviour as the analyte of interest and the emission line should have similar excitation energy and should be the same species, i.e. ion or atom line, as the analyte emission line. 

Emission spectrum Radiation from an atom in an excited state, usually displayed as radiant power vs. wavelength. Each atom or molecule has a unique spectrum. The spectra can be observed as narrow line emission (atomic emission spectra) or as quasi-continuous emissions (molecular emission spectra). A mercury plasma emits both line spectra and continuous spectra simultaneously. 

Line emission Narrow lines of emission from an atom in the excited state the "spikes" observed in spectrometry. 

The value of the ratio Ne/N0 does not imply that all excited atoms return to their initial state as they emit a photon. As the temperature increases, the emission spectrum becomes more complex, particularly due to the emission of lines emanating from ionised atoms (see Fig. 14.3). It thus becomes necessary to have good quality optics in order to use this technique. The corresponding instruments are atomic emission spectrophotometers, which will be discussed in Chapter 15. 

The tail of the plasma formed at the tip of the torch is the spectroscopic source, where the analyte atoms and their ions are thermally ionized and produce emission spectra. The spectra of various elements are detected either sequentially or simultaneously. The optical system of a sequential instrument consists of a single grating spectrometer with a scanning monochromator that provides the sequential detection of the emission spectra lines. Simultaneous optical systems use multichannel detectors and diode arrays that allow the monitoring of multiple emission lines. Sequential instruments have a greater wavelength selection, while simultaneous ones have a better sample throughput. The intensities of each element s characteristic spectral lines, which are proportional to the number of element s atoms, are recorded, and the concentrations are calculated with reference to a calibration standard. 

Wavelength accuracy. In order to evaluate the ability of each system to locate spectral lines, a preliminary wavelength calibration was carred out with the emission spectrum of a mercury pen lamp and then the peak maxima of several atomic lines from an iron hollow cathode lamp were located. The root mean square (RMS) prediction error, which is the difference between the predicted and the observed location of a line, for the vidicon detector system was 1.4 DAC steps. Because it is known from system calibration data that one DAC increment corresponds to 0.0125 mm, the absolute error in position prediction is 0.018 mm. For the image dissector, the RMS prediction error was 7.6 DAC steps, and because one DAC step for this system corresponds to 0.0055 mm, the absolute error in the predicted coordinate is 0.042 mm. The data in Table II represent a comparison of the wavelength position prediction errors for the two detectors. 

In many respects the selectivities of AFS when an atomic line excitation source is used and AAS should be similar, in so far as both depend upon overlap of extremely narrow absorption and emission line profiles. However, there are differences in the extent of interference effects, even for resonance fluorescence,... 

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