High temperature rate constants for OH+ alkanes

摘要

Rate constants for H-atom abstractions by OH radicals from a series of alkanes (propane, n-butane,I-butane and neo-pentane) have been measured at high temperatures with the reflected shock tube techniqueusing multi-pass absorption spectrometric detection of OH radicals at 308 nm. The experiments representthe first direct measurements of these rate constants at T > 1000 K and span a wide T-range, 797–1259 K.The present work utilized 80 optical passes corresponding to a total path length of ～7 m. As a result ofthis increased path length, the high [OH] detection sensitivity permitted pseudo-first-order analysis forunambiguously measuring the total rate constants. The experimental rate constants can be representedin Arrhenius form as,kC3H8＋OH×6:671 －10-11 exp(-1543 K/T)cm3 molecule-1 s-1 (797–1248 K)kn-C4H10＋OH×9:674 －10-11 exp(-1569 K/T)cm3 molecule-1 s-1 (800–1236 K)ki-C4H10＋OH×9:114 －10-11 exp(-1654 K/T)cm3 molecule-1 s-1 (846–1221 K)kneo-C5H12＋OH×1:060 －10-10 exp(-1947 K/T)cm3 molecule-1 s-1 (841–1259 K)The present results have been combined with prior lower-T measurements to generate three-parameterrate expressions that adequately represent the available direct measurements (within 25%) over a wide temperatureregime (250–1250 K). High-level ab-initio electronic structure theory computations of the molecularproperties of reactants, products and transition states have been used to estimate theoretical rateconstants with conventional transition state theory (CTST). The theoretical rate constants are excellentrepresentations of the available experimental data (deviations less than 25%) and thereby offer a reliablemethod for extrapolation to higher-T as well as for extracting branching ratios for primary, secondaryand tertiary abstractions.