Spectroscopic signatures of HHe 2 + and HHe 3

Using two different action spectroscopic techniques, a high-resolution quantum cascade laser operating around 1300 cm −1 and a cryogenic ion trap machine, the proton shuttle motion of the cations HHe 2 + and HHe 3 + has been probed at a nominal temperature of 4 K. For HHe 3 + , the loosely bound character of this complex allowed predissociation spectroscopy to be used, and the observed broad features point to a lifetime of a few ps in the vibrationally excited state. For He–H + –He, a fundamental linear molecule consisting of only three nuclei and four electrons, the method of laser-induced inhibition of complex growth (LIICG) enabled the measurement of three accurate rovibrational transitions, pinning down its molecular parameters for the first time.