The molecular energy levels are labelled by the molecular term symbols.

The ground electronic state is molecular term symbol.

Alternatively it can be written as a molecular term symbol e.g. Σ for dihydrogen.

In the case of less symmetric molecules the molecular term symbol contains the symbol of the group representation to which the molecular electronic state belongs.

Molecular orbital theory predicts two low-lying excited singlet states, denoted by the molecular term symbols Δ and Σ.

The molecular term symbol is a shorthand expression of the angular momenta that characterize the electronic quantum states of a diatomic molecule, which are eigenstates of the electronic molecular Hamiltonian.