Protondeuterium

Protondeuterium, often denoted as pD or $^1_1H$-$^2_1H$, is a hypothetical exotic atom consisting of a proton and a deuteron (the nucleus of deuterium). A deuteron itself is composed of one proton and one neutron. Therefore, in a protondeuterium atom, there would be a total of two protons and one neutron. This atomic species is distinct from deuterium ($^2_1H$), which is a single nucleus containing one proton and one neutron, and also distinct from protium ($^1_1H$), the most common isotope of hydrogen which consists of a single proton.

The formation of protondeuterium would likely require extreme conditions, such as those found in astrophysical environments or within particle accelerators. Theoretical models suggest that such a bound state, if it exists, would be very short-lived due to the electrostatic repulsion between the two positively charged nuclei. Research into such exotic atomic structures is primarily theoretical, exploring the limits of nuclear and atomic physics and the interactions of subatomic particles. The study of such hypothetical systems can provide insights into fundamental forces and the behavior of matter under unusual circumstances. There is no known natural occurrence of stable protondeuterium.