<P> This equation is obtained from combining the Rydberg formula for any hydrogen - like element (shown below) with E = h ν = h c / λ assuming that the principal quantum number n above = n in the Rydberg formula and n = ∞ (principal quantum number of the energy level the electron descends from, when emitting a photon). The Rydberg formula was derived from empirical spectroscopic emission data . </P> <Dl> <Dd> 1 λ = R Z 2 (1 n 1 2 − 1 n 2 2) (\ displaystyle (\ frac (1) (\ lambda)) = RZ ^ (2) \ left ((\ frac (1) (n_ (1) ^ (2))) - (\ frac (1) (n_ (2) ^ (2))) \ right)) </Dd> </Dl> <Dd> 1 λ = R Z 2 (1 n 1 2 − 1 n 2 2) (\ displaystyle (\ frac (1) (\ lambda)) = RZ ^ (2) \ left ((\ frac (1) (n_ (1) ^ (2))) - (\ frac (1) (n_ (2) ^ (2))) \ right)) </Dd> <P> An equivalent formula can be derived quantum mechanically from the time - independent Schrödinger equation with a kinetic energy Hamiltonian operator using a wave function as an eigenfunction to obtain the energy levels as eigenvalues, but the Rydberg constant would be replaced by other fundamental physics constants . </P>

The amount of space occupied by a particle is referred to as the particle’s