The sensitivity of gas-phase models of dense interstellar clouds to changes in dissociative recombination branching ratios.

The approach of Bates to the determination of neutral product branching ratios in ion-electron dissociative recombination reactions has been utilised in conjunction with quantum chemical techniques to redetermine branching ratios for a wide variety of important reactions of this class in dense interstellar clouds. The branching ratios have then been used in a pseudo time-dependent model calculation of the gas phase chemistry of a dark cloud resembling TMC-1 and the results compared with an analogous model containing previously used branching ratios. In general, the changes in branching ratios lead to stronger effects on calculated molecular abundances at steady state than at earlier times and often lead to reductions in the calculated abundances of complex molecules. However, at the so-called "early time" when complex molecule synthesis is most efficient, the abundances of complex molecules are hardly affected by the newly used branching ratios.