Electronic Supporting Information (ESI) Peroxy radical isomerization in the oxida- tion of isoprene

We estimate the CIMS sensitivity for the hydroxyhydroperoxides (ISOPOOH) and hydroperoxyaldehydes (HPALD) from the ion-molecule collision rate, calculated using the parameterization of Su and Chesnavich [1]. This requires knowledge of the average dipole moment and polarizibility of the neutral species. We obtain these parameters for the species of interest from ab initio calulations. For accurate results, all conformers with significant populations at the temperature of interest must be considered. We calculate conformerspecific dipoles for all conformers with a relative population of >1% at T=298K, as estimated from a Boltzman weighting to the conformer energies. The conformer-specific dipoles, weighted by their relative population, are averaged to yield the overall dipole moment for the species of interest. This methodology has been described in more detail by Garden et al. [2]. Table S1 lists the isomer-specific average dipole moments and polarizibilities for the four important ISOPOOH isomers and both