The energy of an ion pair that can assist ion pair separation by ion extraction potential to generate a detectable free ion include translational kinetic energy, vibrational potentialkinetic energy and rotational kinetic energy. For translational kinetic energy to provide the assistance, collision with other molecules or ion pairs is required. Energy in the form of vibration between the two ions in the ion pair is most helpful for the assistance. Vibrational energy in other parts of the ion pair and rotational kinetic energy may provide little assistance. However, different types of internal energy can interconvert through thermal equilibrium.