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