principal series (spectroscopy) on:
[Wikipedia]
[Google]
[Amazon]
In 
The lines are absorption lines when the electron gains energy from an s subshell to a p subshell. When electrons descend in energy they produce an emission spectrum. The term principal came about because this series of lines is observed both in absorption and emission for alkali metal vapours. Other series of lines appear in the emission spectrum only and not in the absorption spectrum, and were named the
atomic emission spectroscopy
Atomic may refer to:
* Of or relating to the atom, the smallest particle of a chemical element that retains its chemical properties
* Atomic physics, the study of the atom
* Atomic Age, also known as the "Atomic Era"
* Atomic scale, distances comp ...
, the principal series is a series of spectral lines caused when electrons move between p orbitals of an atom and the lowest available s orbital. These lines are usually found in the visible and ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
portions of the electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...
. The principal series has given the letter ''p'' to the p atomic orbital
In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any spe ...
and subshell.
The lines are absorption lines when the electron gains energy from an s subshell to a p subshell. When electrons descend in energy they produce an emission spectrum. The term principal came about because this series of lines is observed both in absorption and emission for alkali metal vapours. Other series of lines appear in the emission spectrum only and not in the absorption spectrum, and were named the sharp series
The sharp series is a series of spectral lines in the atomic emission spectrum caused when electrons descend from higher-energy s orbitals of an atom to the lowest available p orbital. The spectral lines include some in the visible light, and they ...
and the 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 inclu ...
based on the appearance of the lines.
References
Atomic physics Emission spectroscopy Absorption spectroscopy {{spectroscopy-stub