Spectral Line Intensities

W. F. Meggers, C. H. Corliss and B. F. Scribner, Tables of Spectral Line Intensities, NBS Monograph 145, Govt. Printing Office, Washington, 1975. 

Organic solvents enhance emitted intensities mainly because of a higher resultant flame temperature (water has a cooling effect), a more rapid rate of feed into the flame because of the generally lower viscosity, and the formation of smaller droplets in the aerosol because of reduced surface tension. The resultant enhancement of spectral line intensity may be 3-to over 100-fold. Conversely, the presence of salts, acids and other dissolved species will depress the intensity of emission from the analyte and underlines the need for careful matching of samples and standards. 

Spectroscopists have always known certain phenomena that are caused by collisions. A well-known example of such a process is the pressure broadening of allowed spectral lines. Pressure broadened lines are, however, not normally considered to be collision-induced, certainly not to that extent to which a specific line intensity may be understood in terms of an individual atomic or molecular dipole transition moment. The definition of collisional induction as we use it here implies a dipole component that arises from the interaction of two or more atoms or molecules, leading at high enough gas density to discernible spectral line intensities in excess of the sum of the absorption of the atoms/molecules of the complex. In other... 

An Ar stabilized direct current (DC) arc plasma at atmospheric pressure was employed to determine Cu, Fe, and Mn in wine [81]. The experimental conditions were optimized by studying the lateral distribution of the spectral line intensities of the elements assessed in aqueous and ethanolic-aqueous solutions. The method was applied to quantify Cu, Fe, and Mn in six wines from three Serbian grape-growing regions and the accuracy was checked by FA AS. 

The following list contains quantities, which can be derived - as a function of time - from spatially resolved spectral line intensity measurements, and the corresponding plasma parameters which can be deduced [16] ... 

Various P-filters are most often used to monochromatize the diffracted beam (e.g. see Figure 3.6, left), but sometimes they are used to eliminate Kp radiation from the incident beam in conventional x-ray sources. The advantages of P-filters are in their simplicity and low cost. The disadvantages include (1) incomplete monochromatization because a small fraction of Kp spectral line intensity always remains in the x-ray beam (2) the intensity of the Ka spectral line is reduced by a factor of two or more, and (3) the effectiveness of a p-filter is low for white x-rays above Ka and it rapidly decreases below Kp. Therefore, p-filters are nearly helpless in eliminating the background, especially when the latter is enhanced by x-ray fluorescence (the filter itself fluoresces due to the true Kp absorption). 

Corliss C. H. and Bozman W. R. (1962) Experimental transition probabilities for spectral lines of 70 elements derived from the NBS tables of spectral line intensities. The wavelengths,... 

Spectroscopic methods depend on the spectral line intensity emitted by the media of interest. Tliese techniques have been used for temperature measurement in high-temperature gases [48]. TTie wavelength involved is generally shorter than those in the infrared band. 

Metal content in zeolite was detected by XRF (X-ray fluorimetry) using a tungsten target. Excitation voltage was 40 kV. Blaze current was 50 mA. The spectral line intensity was recorded on a proportional counter. 

Emission spectroscopy is widely used for both qualitative and quantitative analysis. The high sensitivity and the possible simultaneous excitation of as many as 72 elements, notably metals and metalloids, makes emission spectroscopy especially suited for rapid survey analysis of the elemental content in small samples at the level of 10 /ug/g or less. With control over excitation conditions to maintain constant and reliable atomization and excitation, the spectral line intensities can be used for quantitatively determining concentrations. An analytical curve must be constructed with known standards, and often the ratio of analyte intensity to the intensity of a second element contained in, or added to, the sample (the internal-standard method) is used to improve the precision of quantitative analyses. Preparation of standards for arc and spark techniques requires considerable care to match chemical and physical forms to the sample this is not commonly required for ICP discharge. 

Since the early developments in instrumentation in this country and the success of flame methods for the alkali metals there have been improvements in instrumentation that permit flame excitation to be used for other elements. These improvements have dealt primarily with the use of more efficient aspirators, hotter flames, monochromators (gratings or prisms) for spectral isolation, photomultipliers for increased sensitivity, and recorders for reading spectral line intensities. Today some 45-50 elements can be determined by use of flame excitation procedures. 

Consider the example of the relative intensities of the sodium and D2 lines. Both lines have a common lower level of 3 5i/2- The two upper levels, of almost equal energies, are 3 Pi/2 and 3 P3/2. The numbers of degenerate states are, respectively, 2(1/2) +1=2 and 2(3/2) +1=4. This calculated relative intensity ratio of 1 2 is in accord with experimental spectral line intensity observations. 

Equation (2-28) frequently is modified to relate the spectral line intensity to the population of atoms in the lower energy state (Ni) of the transition being considered. The expression relating the populations of the two states is... 

The usual exit slit also may be dispensed with, if photomultiplier tubes are used to record spectral line intensities, by mounting the phototubes internally. 

For quantitative spectrochemical analysis, using photographic recording, a densitometer is essential since it permits the measurement of relative spectral line intensities. A densitometer for measuring the opacity of a spectral line should have the following characteristics ... 

The interpretation of spectra requires accurate information on spectral line intensities this is essential for quantitative analytical data. Three general procedures are used to obtain this information (1) visual inspection of spectral lines, (2) photographic recording of spectra, and (3) the use of a photocell and associated amplifiers with some type of read-out device. Visual inspection of spectral lines is possible but inconvenient and not very accurate. Photographic recording of spectra is a very common and useful technique since a spectral region may be photographed that includes many spectral lines of many elements. The photoplate also becomes a permanent record of the spectra. 

Light-sensitive phototubes also can be used to determine relative spectral line intensities. Two approaches are used for this purpose. The large, direct reading spectrometers use a battery of phototubes, one for each spectral line desired, located at the individual focal points. Usually the output of the phototube is collected over a specified time interval and stored in a capacitor. After exposure the capacitor is discharged into some type of read-out device. This method integrates the total energy over a time interval to provide a measure of spectral energy. 

A number of wavelength tables with spectral descriptions and relative line intensities are available to the analytical spectroscopist. The most complete and most widely used tables are the MIT Wavelength Tables, which include about 110,000 wavelengths for 87 elements from 2000 to 10,000 A. Spectral line intensities are estimated from 1 to 9000, for excitation in a dc arc and a high-voltage ac spark. The atom lines are designated with the Roman numeral I and the singly ionized lines by the Roman numeral II. 

An extensive study of spectral line intensities has been made at the National Bureau of Standards by Meggers, Corliss, and Scribner. They used copper electrodes and a dc arc to obtain their data on 70 elements. About 39,000 wavelengths are listed. Tables are available by wavelength and also by element. The data are included in the following four monographs available from the U. S. Superintendent of Documents ... 

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