REACTION OF FECH2-2 - PROBING THE [FECH4](+) POTENTIAL-ENERGY SURFACE(+D)

A guided-ion beam mass spectrometer is used to study the reactions FeC H2+ + D-2 and Fe+(D-6,F-4) + CD4, thereby experimentally probing the [ FeCH4](+) potential energy surface(PES). The results obtained are comp ared to recent theoretical results. Experiment and theory agree that d ehydrogenation of methane by Fe+ is hindered by a tight, four-center t ransition state complex. The major discrepancy observed between experi ment and theory is in the height of this barrier, which theory predict s to be 75 kJ/mol (92 kT/mol after correction for zero-point energies) versus our experimental result of 41 +/- 6 kJ/mol. Our results can be interpreted by using phase space theory to help understand how variou s features on the PES control branching ratios among the various chann els observed, including extensive hydrogen scrambling in the FeCH2+ D-2 reaction. Lastly, results for the [FeCH4](+) PES are compared to t hose for the [CoCH4](+) PES obtained in a previous study in order to h elp assess the effect of potential energy surfaces of different spin i n the former case.