For 10 points, identify this quantity simply defined as the intrinsic angular momentum of a particle, which can be plus or minus one-half for an electron.
The long relaxation times observed in forbidden transitions from a triplet degeneracy for this quantity to a singlet state results in phosphorescence. For an electron, the gyromagnetic ratio relates this quantity to magnetic dipole moment, and operators for this observable can be expressed using Pauli matrices. The two beams of silver atoms observed in the Stern-Gerlach experiment correspond to opposite values of this quantity, and electrons in the same orbital must have opposite signs for this quantity according to the Pauli exclusion principle. For 10 points, identify this quantity simply defined as the intrinsic angular momentum of a particle, which can be plus or minus one-half for an electron.
The long relaxation times observed in forbidden transitions from a triplet degeneracy for this quantity to a singlet state results in phosphorescence.
spin [accept spin quantum number until “observable”; accept phosphorescence until "this quantity"]