We have recently built an anion photoelectron imaging instrument to study atmospherically relevant clusters.  Clusters are generated by using pulsed molecular beam valve coupled with either a pulsed electrical discharge or a continuous electron impact source. By seeding the O2 carrier gas with either isoprene or ethanol, several different clusters of (O2)n- �(isoprene)y and (O2)n- �(ethanol)y are generated along with bare (O2)n- clusters.  The photoelectron images of O2-�(ethanol), O4-�(ethanol), and O4-�(isoprene) have been measured.  Comparisons of the bare O2-/ O4-photoelectron spectra to those of the complexes show that addition of isoprene or ethanol results in an increase in electron affinity relative to the bare cluster. In the case of the O4-, complexes with species of differing dipole moments, namely isoprene (0.15 Debye) and ethanol (1.69 Debye), can be compared.  As expected, there is a larger increase in electron affinity when the complexing species has a higher dipole moment, i.e. the electron affinity of O4-�(ethanol) is higher than that of O4-�(isoprene).  The shift to higher electron affinity indicates the anionic oxygen cluster is more stabilized by the presence of a species with a dipole moment.  DFT calculations on the anion and neutral geometries can be used to elucidate the effect of complexing isoprene and ethanol to (O2)n- clusters. By comparing the photoelectron spectra to the DFT results and Franck-Condon simulations, structures for these complexes can either be eliminated or confirmed.

Photoelectron imaging of O2- and O?4?- complexed with isoprene and ethanol

246th National Meeting (2013)

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