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# Hydrogen 1-2 spectral line (121.6 nm, 10.2e V)

Equation 2. "Hydrogen spectral series mnemonic" gives for example from principal quantum number 1 to 2 a difference: $$En​=−13.6eV[221​−121​]=10.2eV (3)$$ which with Planck-Einstein relation gives about 121.6 nm ( Hz), which is a reasonable match with the value of 121.567... from the NIST Atomic Spectra Database.