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

Abstract

The reactions of D/H with n-C4H10 and i-C4H10 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 C2D5I (D-atom precursor, <1ppm) and the alkane of interest in excess (>200ppm), over the T-range 1063–1327K, at pressures ≅0.5atm. D-atom depletion in the present experiments is sensitive only to the reactions,D+n-C4H10→products(A)D+i-C4H10→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,kA=2.11×10-9exp(-5661K/T)cm3molecules-1s-1(1074–1253K)kB=2.57×10-9exp(-5798K/T)cm3molecules-1s-1(1063–1327K)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, kD/kH, are near unity. The theoretical predictions are in good agreement with the experimental results and can be represented by the modified Arrhenius equations,kA,THEORY=6.677×10-17T2.118exp(-2700K/T)cm3molecules-1s-1(500–2000K)kB,THEORY=5.627×10-20T2.934exp(-1225K/T)cm3molecules-1s-1(500–2000K)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-C4H10 and i-C4H10 along with prior studies on C2H6 and C3H8 suggest the applicability of rate rules for H+Alkanes that are based on generic primary, secondary, and tertiary abstraction sites.