excited state

After absorbing energy, an electron may jump from the ground state to a higher energy excited state. Excitations of copper 3d orbitals on the CuO2 plane of a high-Tc superconductor. The ground state (blue) is x–y orbitals; the excited orbitals are in green; the arrows illustrate inelastic x-ray spectroscopy.

In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to an increase in energy level above a chosen starting point, usually the ground state, but sometimes an already excited state. The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit negative temperature).