Activation of C2H6 and C3H8 by gas-phase Mo+:: thermochemistry of Mo- ligand complexes

The kinetic energy dependences of the reactions of Mo+ (S-6) with ethane and propane have been studied using guided ion beam mass spectrometry. No exothermic reactions are observed in these systems, in contrast to results for the neighboring element, Nb+. At slightly elevated energies, dehydrogenation of the two hydrocarbons is observed as the dominant process at low energies in both reaction systems. At high energies, products resulting from both C-H and C-C cleavage processes are appreciable. Modeling of the endothermic reaction cross-sections yields the 0 K bond dissociation energies (in eV) of D-0(MoH) = 2.06 +/- 0.19, D-0(Mo+-H-2) = 0.14 +/- 0.15, D-0(Mo+-CH) = 5.32 +/- 0.14, D-0(Mo+-CH3) 1.57 +/- 0.09, D-0(Mo+-C2H) = 3.25 +/- 0.22, D-0(Mo+-C2H2) 1.87 +/- 0.05, D-0(Mo+-C2H3) = 2.95 +/- 0.15, D-0(Mo+-C2H,) L 0.82 +/- 0.03, D-0(Mo+-C2H5) = 2.09 +/- 0.14, D-0(Mo+-C3H2) = 4.34 +/- 0.21, D-0(Mo+-C3H4) = 2.22 +/- 0.03, and D-0(Mo+-C3H6) : 0.81 +/- 0.05. The ionization energy of MoH is also derived as 7.43 +/- 0.20 eV. The results for Mol are compared to those for the first-row transition-metal congener, Cr+, and the neighboring element, Nb+.