Proton transfer reactions from H 3+ ions to N 2, O 2, and CO molecules

Abstract

The rate constants for proton transfer from H 3 + ions to N 2, O 2, and CO have been measured as function of hydrogen buffer gas partial pressure. The rate constant for proton transfer from H 3 + to N 2 shows a very large pressure dependence, increasing from 1.0 × 10 −9 cm 3/s at low H 2 partial pressures to 1.7 × 10 −9 cm 3/s at high H 2 partial pressures. The rate constants for proton transfer from H 3 + to O 2 and CO are constant with partial pressure of H 2; giving values of 6.4 × 10 −10 cm 3/s and 1.7 × 10 −9 cm 3/s, respectively. The roles of excess vibrational energy in H 3 + ions and of equilibrium between forward and back reaction are discussed. Back reaction is observed only for the reaction of H 3 + ions with O 2, and an equilibrium constant of K = 2.0 ± 0.4 at 298 K has been determined. From these data the proton affinity of O 2 is deduced to be 0.47 ± 0.11 kcal/mole higher than that of H 2.