Some lasers work by exciting atoms of one element and letting these excited atoms collide with atoms of another element and transfer their excitation energy to those atoms. The transfer is most efficient when the separation of energy levels matches in the two species. Given the information in Exercise 1A.17, are there any transitions of He⁺ (including transitions from its excited states) that could be excited by collision with an excited hydrogen atom with an electron in the n = 2 level?

Exercise 1A.17

The energy levels of hydrogenlike one-electron ions of atomic number Z differ from those of hydrogen by a factor of Z².

Predict the wavelength of the transition from n = 2 to n = 1 in He⁺.