Vol. 607
In section 6. Interstellar and circumstellar matter

Search for hydrogen-helium molecular species in space

The search for helium in molecular form has been a long standing challenge in astrophysics. Searches for HeH⁺ have repeatedly come up empty-handed although hydrogenated heavier noble gases have been detected in the interstellar medium. This study proposes an alternative candidate,HeH₃⁺, based on the ubiquitous presence of the H₃⁺ ion in cosmic environments. The authors compute the binding energy, vibrational states, and radiative association rates through two channels. They propose that the HeH⁺ + H₂ dominates by more than four orders of magnitude over the He + H₃⁺ under a wide range of temperatures. Thepaper also provides frequencies to aid in the search for this intriguing molecule whose presence may be important in the context of early universe chemistry.