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

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.