High temperature rate constants for H/D + n-C4H10 and i-C4H10

Abstract The reactions of D/H with n-C 4 H 10 and i-C 4 H 10 have been studied with both shock-tube experiments and ab initio transition state theoretical calculations. D-atom profiles were measured behind reflected shock waves using D-atom atomic resonance absorption spectrometry (ARAS) in mixtures with C 2 D 5 I (D-atom precursor, 200 ppm), over the T-range 1063–1327 K, at pressures ≅0.5 atm. D-atom depletion in the present experiments is sensitive only to the reactions, D + n - C 4 H 10 → products ( A ) D + i - C 4 H 10 → products . ( B ) Simulations of the measured D-atom profiles allow for determinations of total rate constants for the processes (A) and (B). The experimental rate constants are well represented by the Arrhenius equations, k A = 2.11 × 10 - 9 exp ( - 5661 K / T ) cm 3 molecules - 1 s - 1 ( 1074 – 1253 K ) k B = 2.57 × 10 - 9 exp ( - 5798 K / T ) cm 3 molecules - 1 s - 1 ( 1063 – 1327 K ) The title reactions have also been characterized using electronic structure theory at the CCSD(T)/cc-pV∞Z//M06-2X/cc-pvtz level of theory. Over the T-range of the present experiments, the ab initio based transition state theory (TST) kinetics predictions for the isotope effects, k D / k H , are near unity. The theoretical predictions are in good agreement with the experimental results and can be represented by the modified Arrhenius equations, k A,THEORY = 6.677 × 10 - 17 T 2.118 exp ( - 2700 K / T ) cm 3 molecules - 1 s - 1 ( 500 – 2000 K ) k B,THEORY = 5.627 × 10 - 20 T 2.934 exp ( - 1225 K / T ) cm 3 molecules - 1 s - 1 ( 500 – 2000 K ) To our knowledge, the present experiments are the first direct measurements for the title reactions and the rate constants from this combined experimental/theoretical effort are recommended for use in combustion modeling. Results from the present studies on n-C 4 H 10 and i-C 4 H 10 along with prior studies on C 2 H 6 and C 3 H 8 suggest the applicability of rate rules for H + Alkanes that are based on generic primary, secondary, and tertiary abstraction sites.