OBSERVATION OF A MICROWAVE-SPECTRUM OF THE LONG-RANGE HE-CENTER-DOT-CENTER-DOT-CENTER-DOT-N+ COMPLEX

We report the first spectroscopic observation of the HeN+ molecular io n. We use a technique in which a mass-selected ion beam is exposed to tunable microwave radiation, and transitions involving the weakly boun d long-range levels are detected by means of state-selective electric field dissociation, producing N+ fragment ions. Three of the observed microwave transitions exhibit N-14 hyperfine structure, whilst a fourt h transition consists of a single unsplit line. Preliminary observatio ns of Zeeman effects are also described. The results are discussed in terms of molecular energy levels lying close to one or other of the th ree He(S-1) + N+(P-3) dissociation asymptotes, which are split by spin -orbit coupling.