The dioxygenyl ion, O+
2, is a rarely-encountered oxycation in which both oxygen atoms have a formal oxidation state of +⁄₂. It is formally derived from oxygen by the removal of an electron:

The energy change for this process is called the ionization energy of the oxygen molecule. Relative to most molecules, this ionization energy is very high at 1175 kJ/mol. As a result, the scope of the chemistry of O+
2 is quite limited, acting mainly as a 1-electron oxidiser.