Group atomic spectra

Unfortimately, Volume 4 of Charlotte Moore s Atomic Energy Levels has not yet been published, but a complete bibliography of 4f and 5f group atomic spectra has appeared (25). We are not here giving references to individual entities, but merely summarizing ... 

This equation was solved for the hydrogen atom by Vladimir Fock [2,3]. The solution in p space revealed the four-dimensional symmetry responsible for the degeneracy of states with the same n but different I quantum numbers in the hydrogen atom. This is a fine example where the momentum-space perspective led to fresh and deep insight. Fock s work spawned much further research on dynamical groups and spectrum-generating algebras. 

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... 

The proton NMR of this cation showed just one signal for the three methyl groups at 4.15 ppm, quite far downfield for C-Me groups. The spectrum also showed downfield Me groups at 47.5 ppm, but the key evidence that the cation was formed was the shift of the central carbon atom, which came at an amazing 320.6 ppm, way downfield from anything you have met before. This carbon is very deshielded—it is positively charged and extremely electron deficient. 

None of the correlations referred to in the above discussion changes with chain length. The introduction of the sulfur atom does not appear to cause any striking effects. The dipolar ionic form prevails, even with long-chain molecules such as NH2(CH2)ioCOOH. If the amino acid contains an aromatic group, the spectrum will have characteristics different from the usual cases in the region 1600-1500 cm ... 

Polyatomic molecules vibrate in a very complicated way, but, expressed in temis of their normal coordinates, atoms or groups of atoms vibrate sinusoidally in phase, with the same frequency. Each mode of motion functions as an independent hamionic oscillator and, provided certain selection rules are satisfied, contributes a band to the vibrational spectr um. There will be at least as many bands as there are degrees of freedom, but the frequencies of the normal coordinates will dominate the vibrational spectrum for simple molecules. An example is water, which has a pair of infrared absorption maxima centered at about 3780 cm and a single peak at about 1580 cm (nist webbook). 

A diagrammatic illustration of the effect of an isotope pattern on a mass spectrum. The two naturally occurring isotopes of chlorine combine with a methyl group to give methyl chloride. Statistically, because their abundance ratio is 3 1, three Cl isotope atoms combine for each Cl atom. Thus, the ratio of the molecular ion peaks at m/z 50, 52 found for methyl chloride in its mass spectrum will also be in the ratio of 3 1. If nothing had been known about the structure of this compound, the appearance in its mass spectrum of two peaks at m/z 50, 52 (two mass units apart) in a ratio of 3 1 would immediately identify the compound as containing chlorine. 

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