Showing papers by "A. R. Ravishankara published in 1989"

Kinetics and mechanism of hydroxyl radical reaction with methyl hydroperoxide

Abstract: The reaction of hydroxyl radical with methyl hydroperoxide, CH{sub 3}OOH, was investigated in the temperature range 203-423 K by pulsed photolytic generation of OH and detection by laser-induced fluorescence. The rate coefficient for the overall reaction, OH + CH{sub 3}OOH {yields} products (k{sub 1}) was measured by using {sup 18}OH and OD in place of OH. The rate coefficient for the CH{sub 3}O{sub 2} production channel OH + CH{sub 3}OOH {yields} CH{sub 3}O{sub 2} + H{sub 2}O (k{sub 1a}) was obtained by using OH. The channel that yields CH{sub 2}OOH, OH + CH{sub 3}OOH {yields} CH{sub 2}OOH + H{sub 2}O (k{sub 1b}), is not observed when monitoring OH since CH{sub 2}OOH rapidly falls apart to give back OH (and CH{sub 2}O) but is observed when studying the {sup 18}OH or OD reaction with CH{sub 3}OOH. By monitoring OH production in OD + CH{sub 3}OOH reaction at 249 K, the two-channel mechanism was confirmed, and the values for k{sub 1} and k{sub 1a} were also determined. Both reaction 1 and channel 1a show negative activation energies, with k{sub 1} = (2.93 {plus minus} 0.30) {times} 10{sup {minus}12} exp((190 {plus minus} 14)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} (average of {sup 18}OHmore » and OD studies) and k{sub 1a} = (1.78 {plus minus} 0.25) {times} 10{sup {minus}12} exp((220 {plus minus} 21)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, where the indicated error is 1 {sigma}, including estimated systematic errors and {sigma}{sub A} = A{sigma}{sub lnA}. The rate coefficient for the reaction of OD with CH{sub 3}OOD is at least a factor of 2 smaller than that for reaction 1a. The thermal decomposition lifetime for CH{sub 2}OOH to give OH + CH{sub 2}O is deduced to be shorter than 20 {mu}s at 205 K. The mechanism of reaction 1 and the implications of our kinetic and mechanistic results to Earth's atmospheric chemistry are discussed.« less