. . . . . "[2H]2-Water"@en . "Heavy water (deuterium oxide (2H2O ) or D2O) is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium (2H or D, also known as heavy hydrogen), rather than the common hydrogen-1 isotope (1H or H, also called protium) that makes up most of the hydrogen in regular water."@en .