Activation of methane by U+ studied by guided ion beam tandem mass spectrometry and quantum chemistry

Abstract

Reaction pathways of all products formed in the U+ + CH4 (CD4) reaction were explored as a function of kinetic energy using guided ion beam tandem mass spectrometry and quantum chemical calculations. UH+, UC+, UCH+, UCH2+, and UCH3+ (and their perdeuterated analogues) are formed in endothermic reactions. In both systems, the UCH2+ (UCD2+) dehydrogenated product was the dominant product in the low-energy region, whereas the UH+ (UD+) hydride product became predominant at high energies. The kinetic energy behavior of the various products is consistent with a common intermediate of H–U+–CH3 (D–U+–CD3). The kinetic energy dependence of all product cross sections was modeled to obtain experimental bond dissociation energies at 0 K (in eV): D0 (U+–H) = 2.42 ± 0.10, D0 (U+–C) = 3.95 ± 0.12, D0 (U+–CH) = 4.91 ± 0.09, D0 (U+–CH2) = 4.11 ± 0.04, and D0 (U+–CH3) = 2.41 ± 0.09. Quantum chemical calculations using the UCCSD(T) and UB3LYP approaches with the cc-pwCVXZ-PP basis set with MDF-60 pseudopotential for U+ and the aug-cc-pCVXZ and aug-cc-pVXZ (X = T, Q) basis set for carbon and hydrogen, respectively, validate the experimental bond dissociation energies and outline the potential energy surface for all reactions observed. In addition, spin–orbit corrections of the bond energies for all products were calculated at a CASSCF-CASPT2-RASSI level.