Molecular ion:

When a molecule loses or gains electrons, the resulting species is called a molecular ion.

Example:

For example, O₂ when loses one electron forms on but when absorbs an electron it forms O₂⁺ ion. These ions are called molecular ions.

Similarly, N₂ N₂⁺ etc are examples of molecular ions.

Note:

These are short lived species and only exist at high temperature Molecular ions do not for ionic compounds.