# Electron transitions within the same excited state?

• I
• pingaan
In summary, the conversation discusses the possibility of transitions occurring within the same subshell of an electronic dipole. The Laporte Rule and the rule of angular momentum conservation are mentioned as factors that affect the selection of possible transitions. It is noted that the 21 cm hydrogen line is associated with a transition between 1s and 1s, but this is not an electric dipole transition.

#### pingaan

Hi,

I am have trouble finding whether or not the topic is possible.
It concerns an electronic dipole.

I am well familiar with the general rules: https://en.wikipedia.org/wiki/Selection_rule

Is it possible for transitions to occur from e.g. ^4P_1/2 and ^4P_2/3, which are both in n=3?
If they were in two different excited states it would be possible, this I know, but I am unsure of whether or not the rule pi_f = -pi_i plays a role when a possible transition would occur within the state. If it does then it is a matter of pi_f = pi_i, which is not allowed in an electric dipole.

Any help would be greatly appreciated!

Regards,
Toby

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Have you looked into the Laporte Rule? I'm well outside of my expertise area, but it appears to cover transitions within the same subshell.

pingaan
Drakkith said:
Have you looked into the Laporte Rule? I'm well outside of my expertise area, but it appears to cover transitions within the same subshell.

Thanks, I'll have a look at it!

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pingaan said:
Is it possible for transitions to occur from e.g. ^4P_1/2 and ^4P_2/3, which are both in n=3?
No, the first rule is ##\Delta l = \pm 1##. Since it is due to conservation of angular momentum (the spin of the absorbed photon must be transferred to the atom), this is a strong rule, meaning that there aren't many ways of breaking the selection rule even by going beyond the dipole approximation.

topsquark
Drakkith said:
Have you looked into the Laporte Rule? I'm well outside of my expertise area, but it appears to cover transitions within the same subshell.
That's for molecules. I think we are dealing with atomic transitions here.

DrClaude said:
That's for molecules. I think we are dealing with atomic transitions here.
Noted. Thx, DC.

well, the famous 21 cm hydrogen line is associated with the transition between 1s to 1s, the difference comes from parallel to antiparallel aligning of the elecron spon with the proton spin.

Henryk said:
well, the famous 21 cm hydrogen line is associated with the transition between 1s to 1s, the difference comes from parallel to antiparallel aligning of the elecron spon with the proton spin.
Which is not an electric dipole transition.