Rate constants for hydrogen-abstraction by (O) over dotH from n-butanol

Rate constants of hydrogen-atom abstraction from n-butanol by the OH radical have been calculated using variational transition state theory and conventional transition state theory (the latter includes Eckart tunneling corrections) as implemented in Variflex. A stepwise mechanism involving the formation of a reactant complex in the entrance channel and a product complex in the exit channel has been recognized in part of the abstracting processes. A two-transition-state model is used in calculating the individual rate constant for the channels with a barrier-less process in the entrance channel. Variable reaction coordinate transition state theory (VRC-TST) has been used to calculate the rate constants of the barrier-less process. Computed total and individual rate constants, based on a G3 potential energy surface, in the temperature range of 500-2000 K for n-butanol + (O) over dotH are reported as follows (cm(3) mol(-1) s(-1)): k(t) = (4.03 +/- 3.33) X 10(1) x T-3.57 +/- 0.10 exp[(2128 +/- 98)/T] k(alpha) = (4.56 +/- 2.65) x 10(3) x T-2.81 +/- 0.07 exp[(1855 +/- 69)/T] k(beta) = (8.29 +/- 8.94) x 10(-1) x T-3.74 +/- 0.13 exp[(2050 +/- 128)/T] K-gamma = (5.09 +/- 3.66) x 10(1) x T-3.35 +/- 0.09 exp[(2193 +/- 85)/T] k(delta) = (2.15 +/- 0.93) x 10(4) x T2.77 +/--0.05 exp[(-93.3 +/- 51.6)/T] k(oh) = (5.88 +/- 1.85) x 10(2) x T-2.82 +/- 0.04 exp[(294.2 +/- 37.5)/T] The computed individual and total rate constants based on the CCSD(T) potential energy surface over the same temperature range can be similarly expressed as: k(t) = (1.74 +/- 2.20) x 10(1) x T-3.69 +/- 0.16 exp[(1703 +/- 150)/T] k(alpha) = (1.26 +/- 1.49) x 10(3) x T-2.97 +/- 0.05 exp[(1339 +/- 141)/T] k(beta) = (6.80 +/- 7.27) x 10(-1) x T-3.77 +/- 0.13 exp[(1848 +/- 127)/T] k(gamma) = (1.19 +/- 1.18) x T-3.79 +/- 0.12 exp[(2293 +/- 118)/T] k(delta) = (1.75 +/- 0.77) x 10(4) x T-2.79 +/- 0.06 exp[(-220 +/- 52)/T] k(oh) = (5.22 +/- 1.77) x 10(2) x T-2.84 +/- 0.04 exp[(317 +/- 40)/T] The computed total rate constants straddle the very recent shock tube measurements of the total reaction rate at 1017-1221 K, with the G3 results in particularly good agreement with experiment. Abstraction from the terminal methyl group is insignificant for temperatures below 500 K but becomes increasingly dominant at higher temperatures. Abstraction from the alcoholic group is never important. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.