Shock tube/laser absorption measurements of the reaction rates of OH with ethylene and propene

摘要

Reaction rates of hydroxyl (OH) radicals with ethylene (C_2H _4) and propene (C_3H_6) were studied behind reflected shock waves. OH + ethylene → products (rxn 1) rate measurements were conducted in the temperature range 973-1438 K, for pressures from 2 to 10 atm, and for initial concentrations of ethylene of 500, 751, and 1000 ppm. OH + propene → products (rxn 2) rate measurements spanned temperatures of 890-1366 K, pressures near 2.3 atm, and initial propene concentrations near 300 ppm. OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH_3)_3-CO-OH, and monitored by laser absorption near 306.7 nm. Rate constants for the reactions of OH with ethylene and propene were extracted by matching modeled and measured OH concentration time-histories in the reflected shock region. Current data are in excellent agreement with previous studies and extend the temperature range of OH + propene data. Transition state theory calculations using recent ab initio results give excellent agreement with our measurements and other data outside our temperature range. Fits (in units of cm~3/mol/s) to the abstraction channels of OH + ethylene and OH + propene are k_1 = 2.23 × 10~4 (T)~(2.745) exp(-1115 K/T) for 600-2000 K and k_2 = 1.94 × 10~6 (T)~(2.229) exp(-540 K/T) for 700-1500 K, respectively. A rate constant determination for the reaction TBHP → products (rxn 3) was also obtained in the range 745-1014 K using OH data from behind both incident and reflected shock waves. These high-temperature measurements were fit with previous low-temperature data, and the following rate expression (0.6-2.6 atm), applicable over the temperature range 400-1050 K, was obtained: k_3 (1/s) = 8.13 × 10~(-12) (T) ~(7.83) exp(-14598 K/T).