Semiheavy water
Semiheavy water is the result of replacing one of the protium in light water to deuterium. It exists whenever there is water with light hydrogen and deuterium in the mix. This is because hydrogen atoms are rapidly exchanged between water molecules. Water containing 50% H and 50% D in its hydrogen contains about 50% HDO and 25% each of H2O and D2O, in dynamic equilibrium.
In regular water, about 1 molecule in 3,200 is HDO. By comparison, heavy water D2O occurs at a proportion of about 1 molecule in 41 million. This makes semiheavy water far more common than "normal" heavy water.
The freezing point of semiheavy water is close to the freezing point of heavy water.
