Excited state

The ground state of the hydrogen atom has the atom's single electron in the lowest possible orbital (that is, the spherically symmetric "1s" wave function, which, so far, has been demonstrated to have the lowest possible quantum numbers).

Emission of photons from atoms in various excited states leads to an electromagnetic spectrum showing a series of characteristic emission lines (including, in the case of the hydrogen atom, the Lyman, Balmer, Paschen and Brackett series).

A collection of molecules forming a gas can be considered in an excited state if one or more molecules are elevated to kinetic energy levels such that the resulting velocity distribution departs from the equilibrium Boltzmann distribution.

This phenomenon has been studied in the case of a two-dimensional gas in some detail, analyzing the time taken to relax to equilibrium.

[11] A further consequence of excited-state formation may be reaction of the atom or molecule in its excited state, as in photochemistry.

After absorbing energy, an electron may jump from the ground state to a higher energy excited state.
Excitations of copper 3d orbitals on the CuO 2 plane of a high- T c superconductor. The ground state (blue) is x 2 – y 2 orbitals; the excited orbitals are in green; the arrows illustrate inelastic x-ray spectroscopy.