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Singlet state
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<p>In <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>, a singlet state usually refers to a system in which all electrons are paired. The term 'singlet' originally meant a linked set of particles whose net <a href="/facts/Angular_momentum/7TuSVFxq">angular momentum</a> is zero, that is, whose overall <a href="/facts/Spin_quantum_number/5Nh2H8gr">spin quantum number</a> s = 0 {\displaystyle s=0} . As a result, there is only one <a href="/facts/Spectral_line/HuI4Bj5f">spectral line</a> of a singlet state. In contrast, a <a href="/facts/Doublet_state/R5Lr3xtg">doublet state</a> contains one unpaired electron and shows splitting of spectral lines into a doublet, and a <a href="/facts/Triplet_state/sKNlsW1M">triplet state</a> has two unpaired electrons and shows threefold splitting of spectral lines. </p>