Anion photoelectron spectroscopy has proven to be a versatile technique for studying transient neutral species with very fast dynamics, as it obtains information from both the parent negative ion and the reactant neutral molecule. This technique is particularly useful for the study of chemical reactions, where the transition state possess a stable anion. The development of velocity map imaging has greatly improved the spectral resolution and collector efficiency that may be achieved in charged particle detection, to allow for unprecedented detail in the recorded molecular spectra. This seminar will discuss recent efforts to investigate the nature of isomerisation, using High Resolution Photoelectron Imaging (HR-PEI).
A benchmark study of NO2- photodetachment reveals high kinetic energy electron structure that cannot be associated with the ONO C2v isomer. These additional fast electrons have the spectral signature of the Cs peroxy isomer NOO, with spectral analysis providing the first experimental evidence to confirm that the NOO isomer exists as a bound molecule.
A long-standing problem of vinylidene-acetylene isomerisation is also investigated. The photoelectron spectra of the vinylidene anion reveal the presence of forbidden non-totally symmetric vibrational modes, associated with a discrete jump in the anisotropy parameter. This is a consequence of Herzberg-Teller coupling between electronic states, and is essential for isomerisation to occur. Spectral signatures possessing an admixture of both vinylidene and highly excited acetylene local-bender character are discovered, providing a map of the doorway vibrational states through which the isomerization proceeds.
A collection of similar molecules will also be discussed, including the ethynyl coupling mystery and the dicarbon bonding puzzle.