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tokens: for the reaction of C 2+ with normal H 2 . The circles indicate the binned values of the overall reaction rate coefficient k 3 ( T ) obtained in the present study from the measured decay of numbers of detected C 2+ due to the reaction with normal H 2 in the ion trap. The asterisks indicate the binned values of obtained from the measured time evolutions of the number of detected C + product ions. Note that are lower limits for k 3b ( T ). Vertical error bars indicate a statistical error with included uncertainty of the temperature ±5 K, which affects the reactant’s number density. The error band includes a 20% systematic uncertainty of the H 2 reactant pressure measurement as an independent influence. Horizontal error bars include in addition temperature uncertainty ±5 K and the binning of data. By measuring the time evolutions of the number of detected C + ions at different temperatures, we obtained the temperature dependence of the rate coefficient . We use an additional index C + to stress the fact that the value was obtained in the experiment by measuring the production of C + ions. We have in mind that we cannot prove that all the produced C + ions are confined in the ion trap, and a part of them can escape. That is why the measured value is a lower limit for k 3b ( T ). The temperature dependence of the measured reaction rate coefficient for production of C + ions in reaction of C 2+ dications with normal H 2 is also given in Figure 3 . Only a very small fraction of ions corresponding to the production of CH + (see the text above and example in Figure 2 ) was observed, that is why these data are not included in Figure 3 . In Figure 4 , the present k 3 ( T ) is compared with the results of previous experimental studies. Plotted are the present data (binned values as in Figure 3 ) and, for comparison, the values of k 3 ( T ) obtained at 300 K with the SIFT technique by Smith Adams ( 1981 ) and by Viggiano et al. ( 1979 ). We also include the value obtained by Gao Kwong ( 2003 ) at higher collisional temperatures ( T ≈ 2 630 K) using a cylindrical RF ion trap. The value of the Langevin collisional rate coefficient k L for collisions of C 2+ carbon dications with H 2 k L (C 2+ + H 2 ) = 3.2 × 10 −9 cm 3 s −1 is also plotted in Figure 4 . Note that the measured values of k 3 ( T ) are just small fractions of k L , i.e., 4%–5%. Figure 4. Temperature dependence of the reaction rate coefficient k 3 ( T ) of the reaction of C 2+ carbon dications with H 2 , comparison with previous results. The horizontal dashed line indicates the value of the Langevin collisional rate coefficient ( k L = 3.2 × 10 −9 cm 3 s −1 ). The circles indicate the values of k 3 ( T ) obtained in the present study for the reaction of C 2+ carbon dications with normal H 2 . The asterisks indicate values of the reaction rate coefficient , obtained from measured time evolutions of the number of detected C + ions. The values of are lower limits for the actual values of