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| A spin triplet is a set of three quantum states of a system, each with total spin S = 1 (in units of <math>\hbar</math>). The system could consist of a single elementary massive spin 1 particle such as a W or Z boson, or be some multiparticle state with total spin angular momentum of one.
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| In [[physics]], '''[[spin (physics)|spin]]''' is the [[angular momentum]] intrinsic to a body, as opposed to [[angular momentum operator|orbital angular momentum]], which is the motion of its [[center of mass]] about an external point. In [[quantum mechanics]], spin is particularly important for systems at atomic length scales, such as individual [[atoms]], [[protons]], or [[electrons]]. Such particles and the spins of quantum mechanical systems ("particle spin") possess several unusual or non-classical features, and for such systems, spin angular momentum cannot be associated with rotation but instead refers only to the presence of angular momentum.
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| Almost all molecules encountered in daily life exist in a [[singlet state]], but [[molecular oxygen]] is an exception. At room temperature, O<sub>2</sub> exists in a [[Triplet oxygen|triplet state]], which would require the [[forbidden transition]] into a singlet state before a chemical reaction could commence, which makes it kinetically nonreactive despite being thermodynamically a strong oxidant. Photochemical or thermal activation can bring it into [[Singlet oxygen|singlet state]], which is strongly oxidizing also kinetically.
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| __TOC__
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| == Two spin-1/2 particles ==
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| In a system with two spin-1/2 particles - for example the proton and electron in the ground state of hydrogen, measured on a given axis, each particle can be either spin up or spin down so the system has four basis states in all
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| :<math>\uparrow\uparrow,\uparrow\downarrow,\downarrow\uparrow,\downarrow\downarrow</math>
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| using the single particle spins to label the basis states, where the first and second arrow in each combination indicate the spin direction of the first and second particle respectively.
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| More rigorously
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| :<math>
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| |s_1,m_1\rangle|s_2,m_2\rangle=|s_1,m_1\rangle\otimes|s_2,m_2\rangle
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| </math>
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| and since for spin-1/2 particles, the <math>|1/2,m\rangle</math> basis states span a 2-dimensional space, the <math>|1/2,m_1\rangle|1/2,m_2\rangle</math> basis states span a 4-dimensional space.
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| Now the total spin and its projection onto the previously defined axis can be computed using the rules for adding angular momentum in [[quantum mechanics]] using the [[Clebsch–Gordan coefficients]]. In general
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| :<math>|s,m\rangle = \sum_{m_1+m_2=m}C_{m_1m_2m}^{s_1s_2s}|s_1m_1\rangle|s_2m_2\rangle</math>
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| substituting in the four basis states
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| :<math> |1/2,+1/2\rangle\;|1/2,+1/2\rangle\ (\uparrow\uparrow)</math>
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| :<math> |1/2,+1/2\rangle\;|1/2,-1/2\rangle\ (\uparrow\downarrow)</math>
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| :<math> |1/2,-1/2\rangle\;|1/2,+1/2\rangle\ (\downarrow\uparrow)</math>
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| :<math> |1/2,-1/2\rangle\;|1/2,-1/2\rangle\ (\downarrow\downarrow)</math> | |
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| returns the possible values for total spin given along with their representation in the <math>|1/2,\ m_1\rangle|1/2,\ m_2\rangle</math> basis. There are three states with total spin angular momentum 1
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| :<math>
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| \left.\begin{align}
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| |1, 1\rangle &=\; \uparrow\uparrow\\
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| |1, 0\rangle &=\; (\uparrow\downarrow + \downarrow\uparrow)/\sqrt2\\
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| |1,-1\rangle &=\; \downarrow\downarrow
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| \end{align}\;\right\}\quad s=1\quad\mathrm{(triplet)}
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| </math>
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| and a fourth with total spin angular momentum 0.
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| :<math>\left.|0,0\rangle=(\uparrow\downarrow - \downarrow\uparrow)/\sqrt2\;\right\}\quad s=0\quad\mathrm{(singlet)}</math>
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| The result is that a combination of two spin-1/2 particles can carry a total spin of 1 or 0, depending on whether they occupy a triplet or singlet state.
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| == See also ==
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| * [[Singlet state]]
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| * [[Doublet state]]
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| * [[Diradical]]
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| * [[Angular momentum]]
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| * [[Pauli matrices]]
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| * [[Spin multiplicity]]
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| * [[Spin quantum number]]
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| * [[Spin-1/2]]
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| * [[Spin tensor]]
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| * [[Spinor]]
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| ==References==
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| *{{cite book | author=Griffiths, David J.|title=Introduction to Quantum Mechanics (2nd ed.) | publisher=Prentice Hall |year=2004 |isbn=0-13-111892-7}}
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| *{{cite book | author=Shankar, R. | title=Principles of Quantum Mechanics (2nd ed.) | publisher=Springer| year=1994 |isbn=0-306-44790-8 |chapter=chapter 14-Spin}}
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| [[Category:Quantum mechanics]]
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| [[Category:Rotational symmetry]]
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| [[Category:Spectroscopy]]
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Alyson is the name individuals use to call me and I think it seems quite good when you say it. I am really fond of to go to karaoke but I've been taking on new things lately. I've always cherished residing in Alaska. My working day job is an info officer but I've currently utilized for an additional 1.
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