Slow Electron Velocity-Map Imaging (SEVI)

SEVI is a high-resolution photoelectron spectroscopy technique. Photoelectron spectroscopy is a powerful tool due to its relaxed spin selection rules. This allows us to gain information about the energy levels of states that are typically not accessible by traditional absorption spectroscopy. A general example is shown below. When we create a radical anion by attaching an electron to our molecule of interest, we can investigate different spin states, either singlet or triplet in this example, depending on which electron we detach. We can select this based on our photon energy.

These are features general to photoelectron spectroscopy. For SEVI specifically, our high resolution (~10cm-1) grants us vibronic resolution. That is, we are able to discern what vibrations are active in specific electronic transitions. In certain cases, we gain information about what vibrations are coupled to different electronic states, known as vibronic coupling.

In addition, we have the capability to collect action photoelectron spectra of anions. In these experiments, by tuning our photon energy and measuring how many electrons are detached, we can detect the presence of anion excited states. These anion excited state spectra can be very difficult to collect through other methods, and this technique, combined with SEVI and theoretical calculations, allows for us to detail any excited anion states and possibly the manner they detach their electrons.

Recently we have been exploring the electronic structure of different polyacene molecules and their anions. These molecules feature interesting electronic structure, and their optical properties are of great interest to many different fields. Using SEVI, we can elucidate the electronic structure of normally dark states that play important roles in processes that are important for solar cell and OLED design, among many other possibilities.