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

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.