Alkaline Earth Atomic Spectra

The splitting of triplet terms of helium is unusual in two respects. First, multiplets may be inverted and, second, the splittings of the multiplet components do not obey the splitting rule of Equation (7.20). For this reason we shall discuss fine stmcture due to spin-orbit coupling in the context of the alkaline earth atomic spectra where multiplets are usually normal and... 

Although we cannot directly detect HCaOH because it probably has a dissociative UV spectrum [14], we can detect another predicted reaction intermediate in some of our experiments. Mechanism A predicts that the CaH molecule will be present in the Broida oven, and with some oxidants we have detected it by laser-induced fluorescence. The CaH molecule is seen when carboxylic acids such as formic acid are used to make the monocar-boxylates such as Sr02CH [42]. Curiously, CaH is not detected [41] when water or alcohols such as CH3OH are used to make alkoxides such as CaOCH3. More experimental and theoretical work is necessary to establish the chemical mechanisms involved in the reactivity of the alkaline earth atoms. 

Did we predict the number of atoms required to complete additional layers around the metal-coated C(jo correctly Figure 6 shows a spectrum of Qo covered with the largest amount of Ca experimentally possible (note the logarithmic scale). Aside from the edges of A = 32 and a = 104 which we have already discussed, there are additional clear edges at a = 236 and A = 448 (completion of a third layer was also observed at QoSr23g). Note that these values are identical to the ones just predicted above for the completion of the third and fourth layer of metal atoms. We, therefore, feel confident that the alkaline earth metals studied do, in fact, form the distinct layers around a central C50 molecule with the structures depicted in Fig. 5. 

Negative ions were first studied by astrophysicists [59] who recognized that absorption by H is a major source of opacity in the infrared spectrum of the sun. Not all the elements may be able to form negative ions, although their nonexistence is hard to prove. Initially, it was believed (for plausible theoretical reasons) that atoms with closed outer subshells like the alkaline earths could not form negative ions. This has now been shown to be untrue, both experimentally [60] and theoretically [61]. 

The present method to study heavy element compounds in new and our experience is so far limited to atoms and some small molecules. It has the virtue that we can now use the machinery of CASSCF/CASPT2 for the entire periodic system. The method has been tested for all alkaline, alkaline earth, main group, transition metal atoms and in addition for some of the lanthanides and actinides. The results are promising. One example It has recently been possible to assign the electronic spectrum of the UO2 molecule (more than 150 electronic levels were computed) [33]. A drawback is that for the heaviest elements one has to include a large number of electronic states in order to fully account for the effects of spin-orbit coupling. 

Flame atomic emission spectroscopy, also called flame photometry, is based on the measurement of the emission spectrum produced when a solution containing metals or some nonmetals such as halides, sulfur, or phosphorus is introduced into a flame. In early experiments, the detector used was the analyst s eye. Those elements that emitted visible light could be identified qualitatively, and these flame tests were used to confirm the presence of certain elements in the sample, particularly alkali metals and alkaline-earth metals. A list of visible colors emitted by elements in a flame is given in Table 7.1. 

The distribution of the spectral lines of each individual element is not random. It was discovered first empirically and also later shown theoretically that the wavelengths of the lines of the simple atomic spectra can be fitted to simple series formulae with great accuracy. Furthermore, many of the lines in the simple spectra occur in small groups which are called multiplets, such as doublets of the alkali metals or triplets of the alkaline earths. There is also a constant difference between the wavenumbers of the two components of some doublets or two of the three components of some triplets. For example, the two lines of each doublet are separated by 17 cm" in the atomic spectrum of sodium (Table 3). This has been shown by Ritz to be a direct consequence of a general rule named the combination principle. According to this principle, for each atom or molecule there is a set of spectral terms... 

When the atoms of samples are excited to higher electronic energy levels in flames they emit radiation in the visible and UV regions of the electromagnetic spectrum. Emission intensities may be measured to analyze for metals, especially alkali and alkaline earth elements. 

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