Gas-phase metal ion chelation investigated with IRMPD spectroscopy: A brief review of Robert Dunbar's contributions.

With the passing of Prof. Robert C. Dunbar on 31 October 2017, the field of ion chemistry lost one of its modern heroes. Throughout his career in mass spectrometry, two of his main research interests involved the interaction of trapped ions with electromagnetic radiation and the chelation motifs of metal ions with organic ligands. The focus of his early career was on the fundamental processes that take place in molecules upon ultraviolet and infrared excitation. From 2003 to 2017, his scientific interests shifted to more structural questions, notably to resolving the structures and binding motifs of metal ion chelation complexes by application of infrared photodissociation spectroscopy. These experiments were carried out during numerous visits to the (Free Electron Laser for Infrared eXperiments) (FELIX) facility in the Netherlands and were complemented by extensive theoretical investigations by Rob. As a tribute to our friend, we present in this contribution a brief review of this work.