Hydrogen Electron Transitions (Allowed/Forbidden)

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SUMMARY

The discussion focuses on determining whether specific electron transitions in hydrogen are "allowed" or "forbidden" based on transition rules. The transitions analyzed include 2p→2s, 1s→2p, 3d→2p, 3d→1s, and 4s→2p. It is established that the transition 3d→1s is forbidden due to a violation of the angular momentum change rule (Δl > 1). The transition 1s→2p is clarified as allowed, despite concerns about energy conservation, as it can emit photons with zero energy under certain conditions.

PREREQUISITES
  • Understanding of quantum mechanics principles, specifically electron transitions.
  • Familiarity with angular momentum quantum numbers (Δl and Δml).
  • Knowledge of energy level calculations in hydrogen using the formula E = (-2.18*10-18 eV)(1/n12 - 1/n22).
  • Basic grasp of conservation of energy in quantum systems.
NEXT STEPS
  • Study the selection rules for electric dipole transitions in quantum mechanics.
  • Explore the implications of zero-energy photon emission in quantum transitions.
  • Learn about the significance of angular momentum in atomic transitions.
  • Investigate other types of transitions (e.g., magnetic dipole transitions) and their selection rules.
USEFUL FOR

Students and educators in quantum mechanics, physicists analyzing atomic transitions, and anyone interested in the fundamentals of electron behavior in hydrogen atoms.

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Homework Statement


Determine if the electron transitions are "allowed" or "forbidden" using the transition rules:
i. 2p→2s
ii. 1s→2p
iii. 3d→2p
iv. 3d→1s
v. 4s→2p

Homework Equations


Δl = ±1, Δml= 0, ±1
E = (-2.18*10-18eV)(1/n12 - 1/n22)

The Attempt at a Solution


I know iv. is forbidden because Δl is greater than 1, but what about the others? If i. is allowed then the energy is 0eV, which I think is not possible because photos are emitted. May anyone please offer a brief explanation to why it is allowed?
 
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Just write out the angular momentum and energy (quantum number) changes for each transition, and, as you have been doing, check the numbers against the rules. It is usually easier to think in terms of eliminating the transitions that are not allowed.

Good observation that (i) violates conservation of energy.
 
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Simon Bridge said:
Just write out the angular momentum and energy (quantum number) changes for each transition, and, as you have been doing, check the numbers against the rules. It is usually easier to think in terms of eliminating the transitions that are not allowed.

Good observation that (i) violates conservation of energy.

Great, I will follow your steps! I did not know whether (i) is allowed to forbidden, but the explanation is sensible as I did not know it is possible for it to emit photons but with 0eV of energy. Thank you, Simon.
 

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