A nuetral helium atom in is in the excited electronic state, with one electron i

Question

A nuetral helium atom in is in the excited electronic state, with one electron in the (2p) level and the other in the (3d) level. The atom is initally in a region with zero applied magnetic field.

(a) Can the electron in the (3d) level emit a photon and change to the (2p) level? If so, how many different photon energies would you expect to measure? Explain your answer.

(b) A magnetic field of 1.0 Tesla is applied to the atom. Can the electron in the (2p) level emit a photon and change to the (1s) level, with the electron in the (3d) level remaining in the (3d) level? If so, how many different photon energies would you expect to measure? Explain your answer.

I already know the answers. However, there is something I need help understanding. Since the principle quantum number n can only change by +/-1, and the photon energy is determined by the change in n, how can there be multiple photon energies for a single transition?

Explanation / Answer

I guess i got what you want to ask. Look closely at wording of question.

"how many different photon energies would you EXPECT to measure? "

And you are also very correct in your argument. In one transition there will be only one type of photon emission(frequency).

But practically speaking we can't do any experiment with single He atom. So we will have bunch of helium atoms in our sample. And from 3d level to 2p level, it can either jump directly to 2p (few atoms will do such). It will give one type of photon.

In another very likely case , before jumping to 2p state it may choose an intermediate level and than to finally 2p state. So few atoms will choose this way. This way there will be 2 more type of photon emissions.

This is why question is asking what you EXPECT. So you have to choose all possible path electron can take.

I hope this was helpful. Feel free to reach me below for any related questions. Thank you.

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