Shock Tube Measurements of the Rate Constant for the Reaction Ethanol plus OH

The overall rate constant for the reaction ethanol + OH -> products was determined experimentally from 900 to 1270 K behind reflected shock waves. Ethan(18)ol was utilized for these measurements in order to avoid the recycling of OH radicals following H-atom abstraction at the beta-site of ethanol. Similar experiments were also performed with unlabeled ethan(16)ol in order to infer the rate constant that excludes reactivity at the beta-site. The two data sets were used to directly infer the branching ratio for the reaction at the beta-site. Experimental data in the current study and in previous low-temperature studies for the overall rate constant are best fit by the expression k(overall) = 5.07 x 10(5) T[K](2.31) exp(608/T[K]) cm(3) mol(-1) s(-1), valid from 300 to 1300 K. Measurements indicate that the branching ratio of the beta-site is between 20 and 25% at the conditions studied. Pseudo-first-order reaction conditions were generated using tert-butylhydroperoxide (TBHP) as a fast source of (OH)-O-16 with ethanol in excess. (OH)-O-16 mole fraction time-histories were measured using narrow-line width laser absorption near 307 nm. Measurements were performed at the linecenter of the R-22(5.5) transition in the A-X(0,0) band of (OH)-O-16 that does not overlap with any absorption features of (OH)-O-18, thus producing a measurement of the (OH)-O-16 mole fraction that is insensitive to the presence of (OH)-O-18.