Generally the concept of dipole moment is used in neutral system, ie the total positive charge equals to the total negtive charge. Could the concept and also the calculation be used in charged system? For example, NaOH, (Na+)(O-2)(H+), we can calculate its dipole moment. Could I calculate the dipole moment of (OH)- alone? If yes, is there a authoritative definition in some book or papers? Many thanks!