Temperature-Dependent Reaction Kinetics of the Carbanions Cn- and CnH- (n = 2 and 4) with H Atoms in a Cryogenic Ion Trap.

We report on the temperature-dependent reactions of the carbon-chain anions C₂^- and C₄^-, as well as the hydrocarbons C₂H^- and C₄H^- with H atoms in the temperature regime between 8 and 296 K. The experiments have been carried out in a temperature-variable radiofrequency multipole ion trap. From the measured kinetics, we have derived reaction rate coefficients that are constant for all considered systems in the measured temperature regime. For the C₂^-, C₄^-, and C₄H^- anions, the values are about a factor of 2 smaller than the Langevin capture rate coefficient, while for C₂H^-, the measured value agrees with the Langevin value. No theoretical calculations are available at present to explain this. All rate coefficients are in good agreement with previous measurements at room temperature.