Electronic States of Chromium Carbene Ions Characterized by High-resolution Translational Energy Loss Spectroscopy

Rapid progress in experimental methodology has made it possible to generate and study highly reactive organometallic fragments in the gas phase. While experimental investigations have focused mainly on the reactivity and thermochemical stability of such species [l-7], parallel developments in ab initio theory have provided descriptions of the molecular and electronic structures of these molecules [8-: lo]. Transition metal carbenes, species which contain a divalent carbon bonded to a transition metal center, are an example of reactive organometallic fragments which have been the subject of both experimental and theoretical investigations. Ion beam [l-3] and ion cyclotron resonance [4-71 techniques have recently been used to investigate the energetics and reactions of both the coordinately saturated and “bare” transition metal carbenes. In the latter category it has been observed [ 1,4] that the chromium carbene ion, CrCg, can be generated by reaction of electronically excited Cr+ with methane: