tripletn.

1879 Proc. Royal Soc. 30 29 The flame spectrum of magnesium was examined, a green triplet was observed.

1923 Philos. Trans. (Royal Soc.) A. 223 137 In the arc spectra of the alkaline-earth elements, in addition to triplet series, there are series of singlets and also certain ‘intercombination’ lines.

1934 O. W. Richardson Molecular Hydrogen iii. 46 There may be intercombination lines between the singlet and triplet states but if so they must be very faint.

1937 J. W. T. Spinks tr. G. Herzberg Atomic Spectra ii. 79 Terms of the triplet system of He practically do not combine with the terms of the singlet system, and conversely. That is, a prohibition of intercombinations is observed.

1950 J. W. T. Spinks tr. G. Herzberg Spectra Diatomic Molecules (ed. 2) v. 216 Molecules with an even number of electrons have odd multiplicities (singlets, triplets,…) since S is integral.

1977 Nature 3 Nov. 15/1 The Earth has an atmosphere containing diatomic triplet oxygen..essential for life.

1937 Physical Rev. 51 119/2 For an element of the mass [formula follows] certain states in which the neutrons are in the doublet, the protons in the triplet state, exactly coincides [sic] in approximation (1) with a state in which the neutrons are in the quartet, the protons in the singlet state.

1961 M. Gell-Mann in M. Gell-Mann & Y. Ne'eman Eightfold Way (1964) 12 We have a triplet ρ of vector mesons coupled to the isotopic spin current and a singlet vector meson ω⁰ coupled to the hypercharge current.

1968 M. S. Livingston Particle Physics xii. 213 Here [i.e. in SU(3) theory] the basic octet of states is identified with the nucleon, the Σ-particle triplet, the Λ⁰ particle, and the Ξ-particle doublet.

1975 Sci. Amer. Oct. 40/1 The pion is a triplet with an average mass of ·137 GeV and three charge states: +1, 0 and −1.