# L4.2 The uncoupled and coupled basis states for the spectrum | Summary and Q&A

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February 14, 2019
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L4.2 The uncoupled and coupled basis states for the spectrum

## TL;DR

This content discusses the concept of basis states and addition of angular momentum in the hydrogen atom, highlighting the importance of understanding coupled and uncoupled basis states.

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### Q: What are basis states and why are they important in the hydrogen atom?

Basis states are quantum states that uniquely describe the state of an electron in the hydrogen atom. They are important because they allow us to understand and manipulate the properties of electrons, such as angular momentum and spin.

### Q: How are uncoupled basis states described and why is electron spin always 1/2?

Uncoupled basis states are described using quantum numbers n, l, and m to specify the electron's position and orbital angular momentum. Electron spin is always 1/2 because it is an inherent property of electrons and does not change with different orbital angular momentum values.

### Q: What is the difference between coupled and uncoupled basis states?

Coupled basis states involve adding angular momentum, allowing us to express the states as eigenstates of total angular momentum. Uncoupled basis states, on the other hand, do not consider the addition of angular momentum and only focus on the individual values of orbital angular momentum and spin.

### Q: How do coupled basis states in the hydrogen atom correlate with the spectroscopic notation?

Coupled basis states in the hydrogen atom are represented using the spectroscopic notation, which includes the principal quantum number (n), the capital L (representative of the value of l), and the value of j. For example, the state 2p 3/2 corresponds to a coupled basis state with n=2, l=1, and j=3/2.

## Summary & Key Takeaways

• The content introduces the concept of basis states and discusses the importance of considering electron spin and angular momentum in the hydrogen atom.

• Uncoupled basis states are defined using quantum numbers such as n, l, and m to uniquely describe the state of an electron.

• Coupled basis states involve adding angular momentum and expressing states as eigenstates of total angular momentum.