Fundamental series

Originally the series was discovered in the infrared by Fowler and independently by Arno Bergmann.

[1] This resulted in the name Bergmann series used for such a set of lines in a spectrum.

However the name was changed as Bergmann also discovered other series of lines.

[2] Bergmann observed that the lines in the series in the caesium spectrum were double.

His discovery was announced in Contributions to the Knowledge of the Infra-Red Emission Spectra of the Alkalies, Jena 1907.

In 1909 W. M. Hicks produced approximate formulas for the various series and noticed that this series had a simpler formula than the others and thus called it the "fundamental series" and used the letter F.[1][4] The formula that more resembled the hydrogen spectrum calculations was because of a smaller quantum defect.

[7] The two numbers separated by the "−" are called terms, that represent the energy level of an atom.

[8] Lines in the fundamental series are split into compound doublets, due to the D and F subshells having different spin possibilities.

The splitting of the D subshell is very small and that of the F subshell even less so, so the fine structure in the fundamental series is harder to resolve than that in the sharp or diffuse series.

[5] The fundamental series lines for sodium appear in the near infrared.

The fundamental series lines for potassium appear in the near infrared.

The fundamental series lines for rubidium appear in the near infrared.

The valence electron moves from the 4d level as the 3d is contained in an inner shell.