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Determine electronic transitions by the emitted wavelength?

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Sep1-11, 08:42 PM
P: 2
1. The problem statement, all variables and given/known data
What is the electronic transition of He II when it emits 468.6 nm photon.

2. Relevant equations

3. The attempt at a solution
I know it is a pashen-alpha line from googling but I don't know how to find that from this equation with two unknowns. I know the energy levels are discrete so there is probably only one transition that makes this wavelength. Don't know why He II and not He I so I might be missing something.
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Sep1-11, 11:55 PM
HW Helper
P: 10,767
HeI is the neutral He atom, HeII is the once-ionized helium, it has a single electron. The energy levels of HeII can be treated with the Bohr model, with Z=2.

You can find n and m by trial and error. They must be integer numbers in principle. m is the final state, it can be 1, 2, 3,... Find n for each of them. Because of the uncertainty of the wavelength, it will not be an integer number exactly, but it has to be very close to an integer.

Sep1-11, 11:59 PM
P: 2
Thanks for explaining what He II is. I thought there would be some sort of mathematical way to determine the transition without brute force. Oh well.

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