Hydrogen, atomic alpha-line

The transition from n = 3 to = 2 gives rise to a spectral line at 656.3 nm called the hydrogen atom alpha line (Ha). The Ha line is easily observed in the emission from a hydrogen discharge lamp as a red line, but it is not easily observed in the laboratory in absorption ( = 2 to = 3) because so few hydrogen atoms populate the n = 2 level at room temperature that the line is too weak to detect (Exercise 20E). 

It is noted without further comment that Moseley was able to characterize his observed x-ray spectra in such a way that the individual elements are identified purely by their respective atomic numbers without any use of an atomic model. Note again, however, that the denominators in the Qk and Ql expressions are exactly the frequencies of the hydrogenic Lymann and Balmer alpha lines (Moseley s nomenclature) and that therefore Qk and Ql exactly equal the nuclear charge of a one-electron hydrogenic atom which would be deduced from the frequency v of its observed Lymann and Balmer alpha lines2. 

The structure of the polymers was verified by infrared spectra and by spectro-graphic means S). This method, using water samples collected upon combustion of each polymer in a pure oxygen atmosphere, involves essentially the excitation of hydrogen and deuterium atoms by a microwave exciter. The alpha lines in the Balmcr region are resolved and measured by spectrograph, and their intensities are compared with those of standard samples so that the per cent content of deuterium may be determined. 

Figure 25-11 Peptide chain of a protein coiled to form a right-handed alpha helix. Configuration of the helix is maintained by hydrogen bonds, shown as vertical dotted (or solid) lines. The helix on the left shows the detailed atom structure of the peptide chain. The helix on the right is a schematic representation without structural detail. 

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