Dissociative recombination branching ratios and their influence on interstellar clouds

Cross sections and branching ratios for the dissociative recombination (DR) reactions of the astrophysically important ions HN 2 + , HCO + , DOCO + , and SO 2 + at reactant kinetic energies from 1 to 1000 meV have been measured using the CRYRING ion storage ring facility at the Manne Siegbahn Laboratory, Stockholm University. Whereas the break-up of the N-N bond leading to NH + N is the major pathway in the DR of HN 2 + , the analogous reaction in HCO + almost exclusively leads to H and CO. In the DR of both DOCO + and SO 2 + three-body break-up was observed. Inclusion of the newly measured branching ratios into a standard model on dark interstellar clouds leads to an improvement of the predictions of such models, especially concerning the abundances of nitrogen compounds. The impact of these newly found branching ratios and reaction rates on the chemistry of different astronomical environments like dark clouds, circumstellar envelopes and planetary ionospheres, is discussed.