Temperature and pressure dependence of ion–molecule association and dissociation reactions: the N2+ + N2 (+ M) ⇔ N4+ (+ M) reaction†‡
Abstract
Thermal dissociation and the reverse association reactions of molecular ions can be represented within the same framework as unimolecular reactions of neutral molecules. However, because of different intra- and intermolecular interaction potentials, some differences between ionic and neutral systems should also be expected. Starting from these generalities, the present article analyzes the temperature and pressure dependences of dissociation/association rates of ion–molecule reaction systems. The reaction N2+
+ N2
(+ M)
⇔ N4+
(+ M) is considered in particular and falloff curves for this reaction are constructed over the temperature range 5–600 K. Falloff corrections are applied to earlier experiments which allows for a representation of the rate coefficients in terms of a limiting low-pressure rate coefficient kass,0/[N2] cm6 molecule−2 s−1
= 6.8 × 10−29(300 K/T)2.23
− 5.6 × 10−31(300 K/T)3.12, a limiting high-pressure rate coefficient kass,∞/cm3 molecule−1 s−1
= 8.33 × 10−10[1 + 0.069(300 K/T)0.33] and a center broadening factor of the falloff curve Fc
= 0.53 ± 0.05 nearly independent of the temperature. Other examples such as the reactions NH4+
+