I need help to understand the energy transfer mechanism in Helium Neon Gas laser. When helium atom is excited and staying in its metastable state, it is said to have collision with neon atom and thus transfers its 20.61eV energy plus some of its kinetic energy 0.05eV to enable neon atom to reach its metastabel state of 20.66eV. I can't understand this mechanism. To my understanding , as the helium atom decays it must release a photon of 20.61eV. This photon can't be absorbed by neon atom as it does not have such an energy level. So how is this energy transferred? Pl help.