High-Temperature Measurements of the Reactions of OH with Ethylamine and Dimethylamine

Abstract

The overall rate constants of hydroxyl radicals (OH) with ethylamine (EA: CH3CH2NH2) and dimethylamine (DMA: CH3NHCH3) were investigated behind reflected shock waves using UV laser absorption of OH radicals near 306.7 nm. tert-Butyl hydroperoxide (TBHP) was used as the fast source of OH at elevated temperatures. Test gas mixtures of individual amines and TBHP, diluted in argon, were shock-heated to temperatures from 901 to 1368 K at pressures near 1.2 atm. The overall rate constants were determined by fitting the measured OH time-histories with the computed profiles using a detailed mechanism developed by Lucassen et al. (Combust. Flame 2012, 159, 2254-2279). Over the temperature range studied, the measured rate constants can be expressed as kEA+OH = 1.10 × 10(7)·T(1.93) exp(1450/T) cm(3) mol(-1) s(-1), and kDMA+OH = 2.26 × 10(4)·T(2.69) exp(1797/T) cm(3) mol(-1) s(-1). Detailed error analyses were performed to estimate the overall uncertainties of the measured reaction rate constants, and the estimated (2σ) uncertainties were found to be ±31% at 901 K and ±22% at 1368 K for kEA+OH, and ±29% at 925 K and ±21% at 1307 K for kDMA+OH. Variational transition state theory was used to compute the H-abstraction rates by OH for ethylamine and dimethylamine, with the potential energy surface, geometries, frequencies, and electronic energies calculated by Galano and Alvarez-Idaboy (J. Chem. Theory Comput. 2008, 4, 322-327) at CCSD(T)/6-311++G(2d,2p) level of theory. The calculated reaction rate constants are in good agreement with the experimental data.