1. The problem statement, all variables and given/known data Determine the wavelength (in nm, to one decimal place) of the line in the emission spectrum of the He+ ion produced by a transition from n = 3 to n = 1. 2. Relevant equations I used the Rydberg equation for this, although I'm not sure it is the correct one to use. 3. The attempt at a solution Plugging in n1=1 and n2=3, I get an answer of 102.6nm. A search on wikipedia for the Lyman series also shows that transition from n=3 to n=1 is 102.6nm. The solution given, however, is 25.6nm. Obviously I am not understanding the question. Help would be appreciated.