Is spin conserved in heavy metal systems?: Experimental and theoretical studies of the reaction of Re+ with methane

A guided ion beam tandem mass spectrometer is used to study the reactions of atomic Re-187(+) with CH4 and CD4 and collision-induced dissociation (CID) of ReCH4+ with Xe. These studies examine the activation of methane by Re+ in a low-pressure environment free of ligand supports or other reactive species. In the bimolecular reaction, ReCH2+ is efficiently produced in a slightly endothermic process and is the only ionic product observed at low energies, whereas at higher energies, ReH+ dominates the product spectrum. Other products observed include ReC+, ReCH+, and ReCH3+. Modeling of these endothermic reactions yields 0 K bond dissociation energies in eV of D-0(Re+-C) = 5.12 +/- 0.04, D-0(Re+-CH) = 5.84 +/- 0.06, D-0(Re+-CH2) = 4.14 +/- 0.06, D-0(Re+-CH3) = 2.22 +/- 0.13. Analysis of the behavior of the cross sections suggests that formation of ReH+, ReCH2+, and ReCH3+ occurs via an H-Re+-CH3 inter-mediate. CID of ReCH4+ reveals a bond energy of 0.53 +/- 0.15 eV for Re+-CH4. The experimental bond energies compare favorably with theoretical calculations at the B3LYP/HW+/6-311++G(3df,3p) level with the exception of the singly bonded species (ReH+, ReCH3+), where the Becke-half-and-half-LYP functional performs much better. Theoretical calculations also elucidate the reaction pathways for each product and provide their electronic structures. Overall we find that the dehydrogenation reaction, which occurs with an efficiency of 86 +/- 10%, must involve three facile spin changes (2s + 1 = 7 --> 5 --> 3 --> 5) indicating that little hint of spin conservation remains in this heavy-metal system.