State selected reactions of krypton ions with methane Original Research Article

Using a photo-electron product-ion coincidence method, the reactions of Kr+(2P1/2,3/2) ions with methane molecules are studied in the relative kinetic energy range between 0.1 and 1 eV. The relative total cross-sections and the branching ratios for production of CH4+ and CH3+ are determined selectively for the two krypton ions. Using available absolute reaction rates for unselected krypton ions, absolute selective rates are obtained. In addition, a simple model is presented that describes the reactions quantitatively in terms of two distinct mechanisms: (1) reactions via “close collisions”, and (2) reactions via charge exchange in “distant collisions”. Based on this model, evidence for breakdown of the “orbiting transition state theory” for the description of the close collision complex at collision energies above about 0.4 eV, is obtained.