Abstract Photoelectron studies are described for small unstable molecules generated by gas- solid or pyrolysis reactions. The emphasis is on multiply bonded boron compounds including aminoboranes, bis (amino) boranes and oxoboranes, and their electronic and geometric structures. Calculated ionic structures at the MP3/6-31G* level indicate that a distonic radical cation is favoured for aminoborane, H 2 NBH 2. Dehalogenation reactions ...