Sun Hongyan, Vaghjiani Ghanshyam L, Law Chung K
In-Space Propulsion Branch, Rocket Propulsion Division, Aerospace Systems Directorate, Air Force Research Laboratory, AFRL/RQRS, Edwards Air Force Base, California 93524, United States.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, United States.
J Phys Chem A. 2020 May 14;124(19):3747-3753. doi: 10.1021/acs.jpca.0c02389. Epub 2020 Apr 30.
Methylamine radicals (CHNH) and amino radicals (NH) are major products in the early pyrolysis/ignition of monomethylhydrazine (CHNHNH). kinetics of thermal decomposition of CHNH radicals was analyzed by RRKM master equation simulations. It was found that β-scission of the methyl H-atom from CHNH radicals is predominant and fast enough to induce subsequent H-abstraction reactions in CHNHNH to trigger ignition. Consequently, the kinetics of H-abstraction reactions from CHNHNH by H-atoms was further investigated. It was found that the energy barriers for abstraction of the central amine H-atom, two terminal amine H-atoms, and methyl H-atoms are 4.16, 2.95, 5.98, and 8.50 kcal mol, respectively. In units of cm molecule s, the corresponding rate coefficients were found to be = 9.63 × 10 exp(-154.2/), = 2.04 × 10 exp(104.1/), = 1.13 × 10 exp(-416.3/), and = 2.41 × 10 exp(-870.5/), respectively, in the 290-2500 K temperature range. The results reveal that abstraction of the terminal amine H-atom to form -CHNHNH radicals is the dominant channel among the different abstraction channels. At 298 K, the total theoretical H-abstraction rate coefficient, calculated with no adjustable parameters, is 8.16 × 10 cm molecule s, which is in excellent agreement with Vaghjiani's experimental observation of (7.60 ± 1.14) × 10 cm molecule s ( 1997, 101, 4167-4171, DOI: 10.1021/jp964044z).
