Experimental and Theoretical Studies of the Activation of Methane by Ta

A guided-ion-beam tandem mass spectrometer is used to study atomic tantalum cations reacting with CH4 and CD4. Like other third-row transition metal ions, W+, Os+, Ir+, and Pt+, the dehydrogenation reaction to form TaCH2+ + H2 is exothermic. At higher energies, other products, TaH+, TaCH+, and TaCH3+, are observed with TaH+ dominating the product spectrum. Modeling of the endothermic cross sections provides the 0 K bond dissociation energies (in eV) of D0(Ta +−CH) = 5.82 ± 0.16 and D0(Ta+−CH3) = 2.69 ± 0.14 eV. We also examined the reverse reaction, TaCH2+ + H2 → Ta+ + CH4, and its isotopic equivalent, TaCH2+ + D2. By combining the cross sections for the forward and reverse processes, an equilibrium constant for this reaction is derived, from which D0(Ta +−CH2) = 4.81 ± 0.03 eV is obtained. The Ta +−H and Ta +−CH3 experimental bond energies are in reasonable agreement with density functional calculations at the BHLYP/HW+/6-311++G(3df,3p) level of theory, whereas the Ta +−CH and Ta+−CH2 bond energies are p...

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