Reaction of FeCH2++D-2: Probing the [FeCH4](+) potential energy surface

A guided-ion beam mass spectrometer is used to study the reactions FeCH2+ + D-2 and Fe+(D-6,F-4) + CD4, thereby experimentally probing the [FeCH4](+) potential energy surface(PES). The results obtained are compared to recent theoretical results. Experiment and theory agree that dehydrogenation of methane by Fe+ is hindered by a tight, four-center transition state complex. The major discrepancy observed between experiment and theory is in the height of this barrier, which theory predicts 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 various features on the PES control branching ratios among the various channels observed, including extensive hydrogen scrambling in the FeCH2+ + D-2 reaction. Lastly, results for the [FeCH4](+) PES are compared to those for the [CoCH4](+) PES obtained in a previous study in order to help assess the effect of potential energy surfaces of different spin in the former case.