Kinetics of the OH-initiated oxidation of isoprene

Absolute rate coefficients have been determined for the reaction OH + C5H8 (1) and two of its isotopomeric variants. Reaction (1) was studied as a fun ction of temperature and pressure in N-2, N-2 /O-2 and He buffer gases. At room temperature, a rate coefficient, k(1), of (8.56 +/- 0.26)*10(-11) cm(3 ) s(-1) independent of pressure and buffer gas identity was obtained. An Ar rhenius fit to data over the temperature range 250 - 340 K gave a negative activation energy of -666 +/- 150 cal/mol. HO2 production was inferred from observations of radical regeneration in the presence of NO. The absence of a kinetic isotope effect, together with the specificity of radical regener ation, indicates that reaction proceeds via an addition channel with no sig nificant abstraction component. Our rate coefficient for reaction (1) is 15 % lower than the value currently recommenced for atmospheric modeling.