In the He Ne laser, an energetic electron is accelerated by the applied field impacts and excites the He from it's ground state 1s2, to an excited H*, 1s12s1, which has one of the electrons in the 2s orbital. The ground energy of the H3 atom is -79 eV with respect to both electrons isolated at inifinity, which defines the zero energy. Consider the 1s12s1 state. If we neglect the electron-electron interactions, we can calculate the energy of the 1s and 2s electons using the energy for a hydrogenic atom, En=-(Z2/n2)(13.6eV). We can then add the electron-electron interaction energy by assuming that the 1s and 2s electrons are effectively separated by 3a0, which is the difference, 4a0-1a0, between the 1s and 2s Bohr radii. Calculate the overall energy of He* and hence the excitation energy from He to H*. The experimental value is 20.6ev.