DISSOCIATIVE RECOMBINATION AND EXCITATION OF CH5- ABSOLUTE CROSS-SECTIONS AND BRANCHING FRACTIONS( )

The heavy-ion storage ring CRYRING was used to measure the absolute di ssociative recombination and dissociative excitation cross sections fo r collision energies below 50 eV. Deduced thermal rates coefficients a re consistent with previous beams data but are lower by a factor of 3 than the rates measured by means of the flowing afterglow Langmuir pro be technique. A resonant structure in dissociative recombination cross section was found at 9 eV. We have determined the branching fractions in DR of CH5+ below 0.2 eV. The branching is dominated by three-body CH3 + H + H and CH2 + H-2 + H dissociation channels, which occur with branching ratios of approximate to 0.7 and approximate to 0.2, respect ively; thus methane is a minor species among dissociation products. Bo th the measured absolute cross sections and branching in dissociative recombination of CH5+ can have important implications for the models o f dense interstellar clouds and abundance of CH2, CH3 and CH4 in these media.