We report laboratory kinetic studies of isoprene reactions initiated by the
hydroxyl radical OH, using a turbulent flow reactor coupled to chemical io
nization mass spectrometry (CIMS) detection. The rate constants for the rea
ction of isoprene with OH have been measured in the pressure range of 70 to
120 torr at 298 +/- 2 K and are found to be independent of pressure with a
n averaged value of (10.1 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1). The
error limit given is within 1 standard deviation; a systematic error is est
imated to be +/-15%. We also describe direct observation of the OH-isoprene
adduct based on ion-molecule reactions by using the CIMS method. The forma
tion of the OH-isoprene adduct was used to extract the rate constant betwee
n OH and isoprene; within the uncertainty of the experiments the results we
re consistent with those obtained from the observed disappearance of OH. By
monitoring the formation of the OH-isoprene adduct in the presence of oxyg
en molecules, an overall rate constant between OH-isoprene adduct and O-2 h
as been first determined, with an averaged value of (2.8 +/- 0.7) x 10(-15)
cm(3) molecule(-1) s(-1) at 76 torr and an estimated systematic error of /-50%. Atmospheric implications of the present results to the photochemical
oxidation of isoprene are discussed.