Singlet state - singlet state

A state in which the sum of the spin quantum numbers of all electrons in a multi-electron atom or molecule (resultant spin angular momentum S ) is 0. Since the multiplicity of this state (2 S +1) is 1, it is called a singlet state. The ground state of a molecule consisting of an even number of electrons is created by assigning electrons to orbitals starting from the lowest energy level, based on the assembly principle and Pauli principle, but in this case, electrons in the same spatial orbital have antiparallel spins, so S = 0 and the singlet state is often the case. When the highest occupied orbital is degenerate, or when a molecule consisting of an odd number of electrons has a ground state with a large multiplicity. [See alternative term] Triplet state

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

多電子原子や分子の全電子のスピン量子数の和(合成スピン角運動量S)が0である状態．この状態の多重度(2S＋1)は1なので，一重項状態といわれる．偶数個の電子からなる分子の基底状態は，組立て原理とパウリの原理にもとづいて，電子を低いエネルギー準位の軌道から順に帰属していくことによってつくられるが，このとき，同じ空間軌道に入る電子は互いに反平行スピンをもつようになるので，S ＝ 0で，一重項状態になる場合が多い．最高被占軌道が縮退している場合や，奇数個の電子からなる分子の基底状態は，多重度が大きくなる．[別用語参照]三重項状態

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