Principal series (spectroscopy)

In atomic emission spectroscopy, 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 portions of the electromagnetic spectrum.

The principal series has given the letter p to the p atomic orbital and 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.