Motivation: Removal of an electron from a polyanion in the gas-phase leads to a repulsion as the outgoing electron interacts with the remaining anion. The so-called repulsive Coulomb barrier (RCB) is sensitively related to the structure of the molecule.
Philosophy: Photoelectron imaging is ideally suited to probe the RCB and time-resolved photoelectron imaging can be used to probe electron tunneling and geometric changes. Specifically, the outgoing electron is repelled in a direction that avoids the remaining negative charges.
Photoelectron spectra that don’t behave: We discovered that a tell-tale sign of resonant tunneling through a RCB is that the photoelectron spectrum does not shift with photon energy. We have shown that this arises from rapid adiabatic tunneling dynamics that retains the internal energy content following excitation to an excited state.
Photoelectron imaging a rotating RCB: As the RCB is dictated by the molecule’s structure, it follows that any structural evolution should be visible in changes in the photoelectron angular distributions. We have shown this by aligning a dianion with a pump pulse and probing the rotational dephasing.