Theoretical study of isomeric branching in the isoprene-OH reaction: implications to final product yields in isoprene oxidation

The OH initiated oxidation of isoprene is important in tropospheric chemist ry and has major implications for local and regional air quality. The react ion of isoprene with OH has been investigated by ab initio molecular orbita l theory and unimolecular rate theory calculations. We report the energetic s of the four possible adducts and the transition states associated with is omerization, which are energetically comparable to the dissociation of the adduct. We have employed CVTST and RRKM/ME theories based on the ab initio calculations to calculate the rates and branching ratios for the OH-isopren e reaction. The calculated fall-off behavior is consistent with recent expe rimental measurements. (C) 2000 Published by Elsevier Science B.V.