Triplet State

Triplet State

A spin triplet is a set of three quantum states of a system, each with total spin S = 1 (in units of ). 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.

In physics, spin is the angular momentum intrinsic to a body, as opposed to 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.

Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception. At room temperature, O₂ exists in a 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 state, which is strongly oxidizing also kinetically.