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

The dissociative recombination of the methane-derived group, CH + ,...,CH 5 + , 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 + ,...,CH 5 + at 100K are, respectively, 5, 8.7, 12, 12.8 and 12.8*10 -7 cm 3 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 CH 2 + ,...,CH 5 + are also large and roughly equal in magnitude. Like CH + they exhibit a close to E -1 energy dependence below 0.1 eV. For CH 3 + , CH 4 + and CH 5 + the slope of the cross sections increases above 0.1 eV.