Ab initio study of ammonium perchlorate combustion initiation processes: unimolecular decomposition of perchloric acid and the related OH + ClO3 reaction

Abstract

The unimolecular decomposition of HClO ₄ has been investigated at the G2M//B3LYP/6-311+G(3df, 2p) level of theory. Above 500 K, the decomposition process was found to depend strongly on pressure below 200 atm. The rate constants at the high- and low-pressure limits were predicted to be k ₁ ^∞  = 1.5 × 10 ¹⁷ exp(–26500/T) s ^–1 and k ₁ ⁰  = 3.39 × 10 ³⁰ T ^–10.9 exp(–29430/T) cm ³  molecule ^–1  s ^–1 , respectively. Under the atmospheric-pressure condition, the predicted first-order rate coefficient for the temperature range 300–3000 K, k ₁  = 5.0 × 10 ⁵¹ T ^–11.64 exp(–30700/T) s ^–1 , agrees reasonably with experimental data obtained at 550–750 K by different experimental groups. We have also calculated the rate constants for the bimolecular reaction of OH with ClO ₃ producing HClO ₄ by association/stabilization and HO ₂  + ClO ₂ by association/fragmentation. At the high-pressure limit, the rate constants can be given as:k _–1  = 3.2 × 10 ^–10 T ^0.07 exp(–25/T) cm ³  molecule ^–1  s ^–1 and k ₂  = 2.1 × 10 ^–10 T ^0.09 exp(–18/T) cm ³  molecule ^– 1 s ^–1 , respectively, for the temperature range 300–3000 K. Under the atmospheric pressure condition, the OH + ClO ₃ reaction produces predominately the HO ₂  + ClO ₂ products.