Hydrogen deuteride is a diatomic molecule. It is composed of the two isotopes of hydrogen: 1H protium and 2H deuterium.
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H NMR spectrum of a solution of HD (labeled with red bars) and H2 (blue bar). The 1:1:1 triplet arises from the coupling of the 1H nucleus (I = 1/2) to the 2H nucleus ( I = 1).