Merged electron-ion beam experiments. IV. Dissociative recombination for the methane group CH+,...,CH5+

Abstract

The dissociative recombination of the methane-derived group, CH+,...,CH5+, has been measured over the centre-of-mass energy interval 0.03 to 2 eV. Assuming a Maxwellian distribution of the electron velocities, the derived rate coefficients for CH+,...,CH5+ at 100K are, respectively, 5, 8.7, 12, 12.8 and 12.8*10-7 cm3 s-1. The recombination cross section for the diatomic ion CH+ is large. This has far reaching consequences for the theories of molecular formation in interstellar clouds. The cross sections for the polyatomics CH2+,...,CH5+ are also large and roughly equal in magnitude. Like CH+ they exhibit a close to E-1 energy dependence below 0.1 eV. For CH3+, CH4+ and CH5+ the slope of the cross sections increases above 0.1 eV.