Measurement of the equilibrium constant of the reaction HeH + + Ne ⇌ NeH + + He in a selected ion flow tube

Abstract

The reaction HeH + + Ne ⇌ NeH + + He has been studied using a selected ion flow tube apparatus in Aberystwyth. For small Ne flows, the forward reaction can be measured to give a rate constant, 1.25(−9) cm 3 s −1. For large Ne concentrations in the tube the reaction reaches equilibrium, giving an equilibrium constant K = 33 000 ± 20% is a rather conservative estimate of the precision, the data scatter being far less than this. This yields Δ G° = −6.1 ± 0.1 kcal mol −1 or Δ H° = −6.3 ± 0.1 kcal mol −1 = 0.275 ± 0.004 eV. This is equal to the differences in bond energies, D 0(NeH +) − D 0(HeH +) or proton affinities, PA(Ne) − PA(He).