Gadolinium (Gd) Oxide, Carbide, and Carbonyl Cation Bond Energies and Evaluation of the Gd + O → GdO+ + e- Chemi-Ionization Reaction Enthalpy.

Abstract

Guided ion beam mass spectrometry (GIBMS) is used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal gadolinium cation (Gd+) with O2, CO2, and CO and for reactions of GdO+ with CO, O2, and Xe. GdO+ is formed through barrierless and exothermic processes in the reactions of Gd+ with O2 and CO2. All other reactions observed are endothermic, and analyses of their kinetic energy dependent cross sections yield 0 K bond dissociation energies (BDEs) for GdO+, GdC+, and GdCO+. The 0 K BDE for GdO+ is determined from five different reactions to be 7.69 ± 0.10 eV, and this value is combined with literature data to derive the ionization energy (IE) of GdO as 5.82 ± 0.16 eV. Additionally, GdC+ and GdCO+ BDEs of 3.18 ± 0.18 eV and 0.65 ± 0.06 eV are obtained from analysis of the Gd+ reactions with CO and CO2, respectively. Theoretical GdO+, GdC+, and GdCO+ BDEs are calculated for comparison with experiment using various Gd basis sets with an effective core potential and several levels of theory. For calculations that correctly predict a 10D ground state for Gd+, good agreement between theoretical and measured GdC+ and GdCO+ BDEs is obtained, whereas the GdO+ BDE is underestimated in these calculations by about 0.8 eV. Additional BDEs for GdO+ and GdC+ are calculated using triple- and quadruple-ζ correlation consistent all-electron basis sets for Gd. Calculations with these basis sets provide better agreement with experiment for GdO+ but not for GdC+. The measured Gd+ oxide, carbide, and carbonyl BDEs are similar to those for the group 3 metal ions, Sc+ and Y+. This is attributed to similarities in the ground state electronic configurations of these metal ions leading to similar interaction strengths. The experimental GdO+ BDE measured here combined with the known IE of Gd is used to determine an exothermicity of 1.54 ± 0.10 eV for the Gd chemi-ionization reaction with atomic oxygen. This value is consistent with but more precise than previous literature values.