Rate Coefficients For The Endothermic Reactions C+(P-2)+H-2(D-2)->Ch+(Cd+)+H(D) As Functions Of Temperature From 400-1300 K

We have measured the bimolecular rate coefficients for the reactions of C+(P-2) with H-2 and D-2 as functions of temperature from 400 to 1300 K using a high temperature flowing afterglow apparatus. The temperature dependences of these rate coefficients are accurately fit by the Arrhenius equation, with activation energies equal within experimental uncertainty to the reaction endothermicities. Internal energy dependences have been deduced by combining the present data with previous drift tube and ion beam measurements. We found that reactant rotational energy and translational energy an equally effective in surmounting the energy barrier to reaction, and that vibrational excitation of the neutral reactant to the upsilon=1 state enhances the rate coefficients by a factor of similar to 1000 for the reaction with H-2 and by similar to 6000 for the reaction with D-2 at temperatures of 800 and 500 K, respectively. This vibrational enhancement is larger than the enhancement that would be produced if the same amount of energy were put into translational and/or rotational modes of the reactants. In addition, rate coefficients have been derived for the three-body association reaction of C+(P-2) with H-2 in a helium buffer over the temperature range 300-600 K. (C) 1997 American Institute of Physics.