1. The problem statement, all variables and given/known data Is the following transition allowed? [4,3,0,1/2] -> [4,2,1, -1/2] If so, find the energy involved and whether the photon is absorbed or emitted for the hydrogen atom. 2. Relevant equations Selection rules for allowed transitions: [tex]\Delta[/tex]n = anything [tex]\Delta[/tex]l =[tex]\pm[/tex]1 [tex]\Delta[/tex]ml = 0 or [tex]\pm[/tex]1 3. The attempt at a solution [tex]\Delta[/tex] n = 4-4 = 0 [tex]\Delta[/tex] l = 3-2 = 1 [tex]\Delta[/tex]ml = 0-1= -1 So all of the transitions are allowed, but it doesn't quite make sense to me. There is no energy involved, because [tex]\Delta[/tex] n = 0, which means that this electron just suddenly spontaneously decided to be in a different configuration, can it do that? (I also checked and it looks like both of the states are allowed...) Can it do that, am I missing something? Thanks for your help!