Atom line

The trends in chemical and physical properties of the elements described beautifully in the periodic table and the ability of early spectroscopists to fit atomic line spectra by simple mathematical formulas and to interpret atomic electronic states in terms of empirical quantum numbers provide compelling evidence that some relatively simple framework must exist for understanding the electronic structures of all atoms. The great predictive power of the concept of atomic valence further suggests that molecular electronic structure should be understandable in terms of those of the constituent atoms. 

Figure 12.10 Diagram showing two subunits of the channel, illustrating the way the selectivity filter is formed. Main-chain atoms line the walls of this narrow passage with carbonyl oxygen atoms pointing into the pore, forming binding sites for ions. (Adapted from D.A. Doyle et al., Sdence 280 69-77, 1998.)...

Click Coached Problems for a self-study module on atomic line spectra. 

During the first twenty years or so of this century, an incredibly detailed understanding of atomic line spectra was built up with the application of the, then new, quantum theory. Indeed, the development of quantum theory came about in part by the need to understand these spectral properties. We shall have to review some basic features of the theory of atomic spectra for our present purposes, but we shall leave it for the moment. 

ICP-AES and ICP-MS analyses are hampered in almost all cases by the occurrence of sample matrix effects. The origins of these effects are manifold, and have been traced partly to physical and chemical aerosol modifications inside sample introduction components (nebulisation effects). Matrix effects in ICP-AES may also be attributed to effects in the plasma, resulting from easily ionised elements and spectral background interferences (most important source of systematic errors). Atomic lines are usually more sensitive to matrix effects than are ionic lines. There exist several options to overcome matrix interferences in multi-element analysis by means of ICP-AES/MS, namely ... 

Water and sludge Acidify sample measure absorption at 196.0 nm using the selenium atomic line. AAS 0.25 NR Parvinen and Lajunen 1994... 

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. 

The spectra have been reduced with the GIRAFFE BLDRS pipeline developed at the Geneva Observatory. EW have been measured with DAOSPEC [2], based on a linelist produced with the Vienna Atomic Line Database (VALD) [3]. Preliminary estimates of the stellar parameters Te//, log g, vt and [M/H] have been obtained from the WFI photometry published by [4] and the color-temperature calibration by [5]. MARCS model stellar atmospheres [6] have been... 

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. 

The nature of the clustered phase is not well understood. One possible interpretation is that a cluster is composed of a relaxed divacancy whose inner surface is dressed with hydrogens however there is no direct NMR data which supports this identification (Reimer and Petrich, 1988). Alternatively, it has been suggested that the broad component of the NMR spectrum arises from hydrogen atoms lined up alone microtubular structural defects (Chenevas-Paule and Bourret, 1983). 

Fig. 3.18. Synthetic spectrum of a red giant, Tes = 4500 K, log g = 2.25 in the region of the strong Mg i b lines (see Fig. 3.9). The upper spectrum is the same with atomic lines switched off and shows molecular bands of MgH. The horizontal lines show the central and side bands of the Lick Mg2 index. Adapted from Mould (1978).

Energy level diagrams for the easily excited atomic lines of lithium, sodium, potassium and rubidium. Wavelengths are given in nanometres for the spectral lines produced by transitions between the different levels. The ionization potential is indicated by the dashed line above the respective diagrams. 

X-ray transitions in the molybdenum atom. Lines are designated by the letter referring to the lower quantum group and a where An = - 1 and P where An = - 2. 

Incomplete dissociation of alkaline-earth oxides and hydroxides often causes unwanted molecular bands to be stronger than atomic lines. This can often be cured by altering flame temperatures or fuel/oxidant ratio, to shift the equilibrium in the desired direction. 

The substrate also played an important role in controlling the movement of nanoparticles at moderate temperatures before the nanoparticles melt. This can be clearly seen in Fig. 10.5 where nanoparticles are aligned with the atomic lines on Si (001). In addition, H2 and SAN together may play an even more important role in the catalysis of SiNW, as shown below. 

It was found that the solids concentration in atomizer line conductivity had risen at the end of DI-3. A full explanation of this anomaly is not now available. There is some information to suggest that the behavior is due to changing pH in the DI output, even though the conductivity or dissolved solids of the DI output water remained good. 

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. 

However, atomic lines are not infinitely thin as would be expected and their width is discussed by talking about half-width (Av cm ), illustrated in Fig. 4.2a. 

Profile of an atomic line (a) the half width Av is the width of the line when k = l/2k (b) the effect of self-absorption as the concentration of atoms increases from 1 to 5. 

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. 

---