It sounds like a fossil molecule, but no, not exactly:
Known as a helium hydride ion (HeH+), this conglomeration of Big Bang leftovers is just a helium atom and a hydrogen nucleus, aka a proton. Scientists had expected to find it throughout the cosmos, but for decades they couldn’t spot it anywhere. (Researchers managed to create some in 1925, so they knew at least it could exist.)
Bill Andrews, “Scientists Find the Universe’s First Molecule” at Discover Magazine
Last April Astronomers finally detected some of the stuff in a gas cloud about 2900 light years from Earth.
Here’s the story, which was one of Discover’s stories of the year, from last April:
As atoms combined to form the first molecules, the Universe was finally able to cool and began to take shape. Astrophysicists have inferred that HeH+ was this first, primordial molecule.
Once cooling began, hydrogen atoms could interact with HeH+, leading to the creation of molecular hydrogen — the molecule primarily responsible for the formation of the first stars.
News Staff, “Helium Hydride Ion Spotted in Space for First Time” at SciNews
Paper. (paywall)