The fundamental series is a set of
spectral line
A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...
s in a set caused by transition between d and f
orbitals in atoms.
Originally the series was discovered in the infrared by Fowler and independently by
Arno Bergmann.
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. And other discoverers also established other such series. They became known as the fundamental series.
Bergmann observed lithium at 5347 cm
−1, sodium at 5416 cm
−1 potassium at 6592 cm
−1.
[ 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.] Carl Runge
Carl David Tolmé Runge (; 30 August 1856 – 3 January 1927) was a German mathematician, physicist, and spectroscopist.
He was co-developer and co-eponym of the Runge–Kutta method (), in the field of what is today known as numerical analysi ...
called this series the "new series". He predicted that the lines of potassium and rubidium would be in pairs.[ He expressed the frequencies of the series lines by a formula and predicted a connection of the series limit to the other known series. 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.]
The formula that more resembled the hydrogen spectrum calculations was because of a smaller quantum defect. There is no physical basis to call this fundamental. The fundamental series was described as badly-named.[ ] It is the last spectroscopic series to have a special designation.[ The next series involving transitions between F and G subshells is known as the FG series.][
Frequencies of the lines in the series are given by this formula:
''R'' is the ]Rydberg constant
In spectroscopy, the Rydberg constant, symbol R_\infty for
heavy atoms or R_\text for hydrogen, named after the Swedish physicist Johannes Rydberg, is a physical constant relating to the electromagnetic spectra of an atom. The constant first ...
, is the series limit, represented by ''3D'', and is represented by ''mF''. A shortened formula is then given by with values of m being integers from 4 upwards.[ The two numbers separated by the "−" are called terms, that represent the energy level of an atom.
The limit of the fundamental series is the same as the 3D level.][
The terms can have different designations, mF for single line systems, mΦ for doublets and mf for triplets.]
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
The diffuse series is a series of spectral lines in the atomic emission spectrum caused when electrons jump between the lowest p orbital and d orbitals of an atom. The total orbital angular momentum changes between 1 and 2. The spectral lines inc ...
.
Lithium
The quantum defect for lithium is 0.[
]
Sodium
The fundamental series lines for sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
appear in the near infrared.
Potassium
The fundamental series lines for potassium
Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
appear in the near infrared.
Rubidium
The fundamental series lines for rubidium
Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...
appear in the near infrared. The valence electron moves from the 4''d'' level as the 3''d'' is contained in an inner shell. They were observed by R von Lamb.
Relevant energy levels are 4''p''64''d'' ''j''=5/2 19,355.282 cm−1 and ''j''=3/2 19,355.623 cm−1, and the first ''f'' levels at 4''p''64''f'' ''j''=5/2 26,792.185 cm−1 and ''j''=7/2 26,792.169 cm−1.[ ]
Caesium
References
{{Reflist
Spectroscopy
Atomic physics
Emission spectroscopy