Gadolinium cation (Gd) reaction with O: Potential energy surface mapped experimentally and with theory.

Guided ion beam tandem mass spectrometry is used to measure the kinetic energy dependent cross sections for reactions of the lanthanide metal gadolinium cation (Gd) and GdO with O and for collision-induced dissociation (CID) of GdO with Xe. Gd reacts with O in an exothermic and barrierless reaction to form GdO and O. GdO is also formed in this reaction, but this product ion is formed in a sequential reaction, as verified by pressure dependent measurements and comparison with the results for the reaction of GdO with O. The CID experiments of GdO indicate the presence of two GdO precursor ion populations, assigned to a weakly bound oxygen molecule adduct (Gd-O) and an inserted cyclic Gd dioxide species (O-Gd-O). Analysis of the resulting product ion cross sections yields bond dissociation energies (BDEs, D) for Gd-O and OGd-O, where the latter BDE is also independently measured in an exchange reaction between GdO and O. The CID experiments also provide the energy of the barrier for the rearrangement of the Gd-O adduct to the inserted O-Gd-O structure (as identified by loss of a single oxygen atom). The thermochemistry measured here yields D(OGd-O) = 2.86 ± 0.08 eV, D(Gd-O) = 0.75 ± 0.11 eV, and a barrier height relative to Gd-O of 0.31 ± 0.07 eV. These data are sufficient to characterize in some detail the potential energy surface of the Gd reaction with O entirely from experiment. Theoretical calculations are performed for comparison with the experimental energetics and for further insight into the reaction mechanisms.