text: The neutral molecule can be formed in a low pressure gas discharge tube.
  A neutral beam of H can be formed from a beam of  ions passing through gaseous potassium, which donates an electron to the ion, forming K. Other gaseous alkali metals, such as caesium, can also be used to donate electrons.  ions can be made in a duoplasmatron where an electric discharge passed through low pressure molecular hydrogen.  This causes some H to become . Then H +    + H. The reaction is exothermic with an energy of 1.7 eV, so the ions produced are hot with much vibrational energy. These can cool down via collisions with cooler gas if the pressure is high enough. This is significant because strongly vibrating ions produce strongly vibrating neutral molecules when neutralised according to the Franck–Condon principle.