Why is a triplet state said to have anti-parallel spins?

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In summary, the triplet state can have three spin eigenfunctions, (+1/2,+1/2), (-1/2,-1/2), and (1/squareroot(2))*((+1/2,-1/2)+(-1/2,+1/2)). The first two represent electrons with parallel spins, while the third represents electrons with antiparallel spins. This is because the triplet state can have total z-projected momentum of 1, 0, or -1. The singlet state, on the other hand, has only antiparallel spins. The distinction between the two states is the sign they mix with.
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Aniket1
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The triplet state can have one of the following three spin eigenfunctions:
(+1/2,+1/2)
(-1/2,-1/2)
(1/squareroot(2))*((+1/2,-1/2)+(-1/2,+1/2))
I read that this state has electrons with parallel spins (which i assume is the z component of the spin angular momentum)
I didn't understand how the third eigenfunction represents electrons with antiparallel spins when it assigns +1/2 to one electron and -1/2 to the other.
 
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  • #2
The triplet state can either have total z-projected momentum of 1,0,-1. So when the electrons have parallel spins that can be state 1 or -1. When they have anti-parallel spins that is state 0. +1/2 and -1/2 are spins that point in the opposite direction, so that is the definition of anti-parallel (for a QM spin where you only have one quantization axis).
 
  • #3
If +1/2 and -1/2 are spins pointing in opposite directions, the third spin eigenfunction (which has been mentioned in the question) should represent electrons with opposite spins ( or am i making a mistake in interpretating the function?). But it is an eigenfunction of the triplet state. And triplet states have parallel spins. So where is the flaw in the argument?
Also since the total z-projected momentum can be zero for a triplet state, the spins of the electrons in this case will be in opposite directions to cancel each other.
So what do we mean by parallel and antiparallel spins in triplet and singlet states?
 
  • #4
No triplet states don't just have parallel spins. The triplet state with m_z = 0 has antiparallel spins. But a pair of parallel spins must be a triplet state because it cannot be a singlet state. The singlet state has only antiparallel spins. The distinction between the singlet state | 0 0 > and the triplet state |1 0> is the sign the two states mix with.
 
  • #5
Thanks..
 

FAQ: Why is a triplet state said to have anti-parallel spins?

1. What is a triplet state?

A triplet state is one of the three possible electronic states that an atom or molecule can have. It is characterized by two unpaired electrons with parallel spins.

2. Why is a triplet state important?

A triplet state is important because it plays a crucial role in many chemical reactions and processes, particularly in organic chemistry. It is also significant in the study of molecular structure and properties.

3. What are anti-parallel spins?

Anti-parallel spins refer to the orientation of the electrons' spin in a triplet state, where they are aligned in opposite directions. This is in contrast to parallel spins, where the electrons' spin are aligned in the same direction.

4. How is a triplet state different from a singlet state?

A triplet state is different from a singlet state in terms of the number of unpaired electrons. A triplet state has two unpaired electrons with parallel spins, while a singlet state has no unpaired electrons.

5. What is the significance of anti-parallel spins in a triplet state?

The presence of anti-parallel spins in a triplet state leads to a lower energy state, making it more stable compared to a singlet state. This allows for a higher probability of the triplet state being involved in chemical reactions and processes.

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