ACTIVATION OF C2H6, C3H8, AND C-C3H6 BY GAS-PHASE RH+ AND THE THERMOCHEMISTRY OF RH-LIGAND COMPLEXES

The reactions of Rh+ with C2H6, C3H8, and c-C3H6 at hyperthermal energies have been studied by using guided ion beam mass spectrometry. If is found that dehydrogenation is efficient and the dominant process at low energies in all three reaction systems. At high energies, C-H cleavage processes dominate the product spectrum for the reactions of Rh+ with ethane and propane. C-C bond cleavage is a dominant process in the cyclopropane system. The reactions of Rh+ are compared with those of Co+ and the differences in behavior and mechanism are discussed in some detail. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies (in eV) of D-0(Rh-H) = 2.42 +/- 0.06, D-0(Rh+-C) = 4.25 +/- 0.18, D-0(Rh+-CH) = 4.60 +/- 0.12, D-0(Rh+-CH2) = 3.69 +/- 0.08, D-0(Rh+-CH3)= 1.47 +/- 0.06, D-0(Rh+-C2H2) = 1.67 +/- 0.03, D-0(Rh+-C2H5)= 1.80 +/- 0.18, and D-0(Rh+-C3H4) = 2.3 +/- 0.2 and set lower limits of D-0(Rh+-C2H4) > 1.34 and D-0(Rh+-C3H6) > 1.22 eV.