OBSERVATION OF A MICROWAVE-SPECTRUM OF THE LONG-RANGE HE-CENTER-DOT-CENTER-DOT-CENTER-DOT-H-2(+) COMPLEX

We report the first spectroscopic observations of the HeH2+ molecular ion. We use an ion beam technique in which mass-selected ions are expo sed to microwave radiation, and transitions involving weakly bound lon g-range levels are detected by means of state-selective electric field dissociation. One of the observed transitions exhibits complex proton nuclear hyperfine structure; another shows a simple field-free spectr um but extensive Zeeman structure in the presence of an applied magnet ic field, The results are discussed in terms of coupled-channel calcul ations using a recent ab initio potential surface.