High-resolution leak-out spectroscopy of HHe.

Applying a novel and universal action spectroscopic technique, called leak-out spectroscopy, this paper revisits the proton shuttle motion of the symmetric linear molecule He-H-He. For this, a 4 K cryogenic ion trap apparatus has been combined with a high-resolution quantum cascade laser operating around 1300 cm. Seven rovibrational lines of this fundamental three-nucleus-four-electron system are recorded, demonstrating the suitability of the leak-out method for such fundamental hydrogen-helium cations.