Photoelectron imaging of multiply charged anions: Effects of intramolecular Coulomb repulsion and photoelectron kinetic energies on photoelectron angular distributions.

Multiply charged anions possess strong intramolecular Coulomb repulsion (ICR), which has been shown to dictate photoelectron angular distributions (PADs) using photoelectron imaging. Here we report the effects of photoelectron kinetic energies on the PADs of multiply charged anions. Photoelectron images on a series of dicarboxylate dianions, (-)O(2)C(CH(2))(n)CO(2) (-) (D(n) (2-), n=3-11) have been measured at two photon energies, 532 and 266 nm. The first photoemission band of D(n) (2-), which is a perpendicular transition in the absence of the ICR, comes from electron detachment of an O lone pair orbital on the -CO(2) (-) end groups. Recent photoelectron imaging studies at 355 nm show that the PADs of D(n) (2-) peak in the directions parallel to the laser polarization for small n due to the ICR, which directs the outgoing electrons along the molecular axis. The current data show much stronger parallel peaking at 532 nm, but much weaker parallel peaking in the 266 nm data, relative to the 355 nm data. These observations indicate that the ICR has greater influence on the trajectories of slow photoelectrons and much reduced effects on faster photoelectrons. This study demonstrates that the PADs of multiply charged anions depend on the interplay between ICR and the outgoing photoelectron kinetic energies.