DYNAMICS OF NON-VALENCE STATES IN ANIONS

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Motivation: Non-valence states in neutrals (Rydberg states) are common and known to be intimately involved in valence states’ dynamical evolution. One might thus imagine the same to be so for anions. However, essentially nothing is known about such dynamics.

Philosophy: Photoelectron imaging is ideally suited to probe non-valence states because: (1) their low binding energy can be directly measured; (2) their spectral signature is a sharp peak because of the similarity between the non-valence anion surface and that of the final neutral state; and (3) they have a distinct photoelectron anisotropy because the initial orbital is typically of s-character. We have now found evidence for the participation of non-valence states in many anionic systems suggesting that these are more common than previously appreciated.    

Valence to non-valence dynamics: Valence states excited near the detachment threshold can evolve into non-valence states. This has been observed in radical anion clusters and in small anionic chromophores. The valence to non-valence dynamics are typically very fast and the non-valence state subsequently decays by mode-specific vibrational autodetachment, which can be clearly evidenced in photoelectron spectra.

Non-valence to valence dynamics: Non-valence states can serve as a doorway to electron attachment. We have probed an entire electron-molecule reaction involving the initial population of a non-valence state and its evolution to a valence state in real-time. Both the nuclear and electronic structure was probed evidencing all stages of the process.

Non-valence correlation-bound state: Non-valence states in anions are most commonly bound by electrostatic forces (i.e. electron interaction with permanent dipole-moment or quadrupole-moment). However, electrons can also be bound by correlation forces as predicted by theory. We have presented the first spectroscopic observation of a non-valence state predominantly bound by correlation forces.