Gerade

Possible eigenvalues

For electronic wavefunctions, even states are usually indicated by a subscript g for gerade (German: even) and odd states by a subscript u for ungerade (German: odd). For example, the lowest energy level of the hydrogen molecule ion (H+2) is labelled ${\displaystyle 1\sigma _{g}}$ and the next-closest (higher) energy level is labelled ${\displaystyle 1\sigma _{u}}$.