UC Berkeley

The anion slow photoelectron velocity-map imaging (SEVI) technique, a high resolution (~1 cm^-1) variant of anion photoelectron spectroscopy, is applied to the study of open-shell anions and neutral species. First, SEVI is used to study the C_nH (n=5-9), C_2nN (n=1-3), C_nO (n=2-3) and C_nS (n=2-3) heteroatom doped carbon clusters. The SEVI spectra are assigned with the help of electronic structure calculations and Franck-Condon simulations. Precise electron affinities, term energies and vibrational frequencies are determined for these species. These studies also yield evidence of vibronic coupling in the ground states of C₆H, C₈H, C₉H and CCS. Futhermore, it is found that the ground states of the C₅H^-;, C₇H^-;, C₇H^-;, C₄N^-; and C₆N^-; anions are linear triplet sigma states, contrary to previous theoretical studies that reported bent structures.

In addition, the strong vibronic coupling between the very close-lying ²A₁ and ²B₂ states of the HCO₂ and DCO₂ radicals is studied using SEVI. The complex photodetachment spectra are simulated and assigned using a quasidiabatic Hamiltonian approach. The strong vibronic coupling is highlighted by the observation of several nominally forbidden transitions.

The SEVI technique is also applied to the study of the weakly bound ArO and KrO van der Waals complexes. The interaction potential and spin-orbit splitting of the neutral and anion states are determined and compared with high-level electronic structure calculations. Finally, the SEVI spectra of the ClH₂^-; and ClD₂^-; anions are used to characterized the electronic and nuclear coupling in the pre-reactive region of the Cl(²P)+H₂ reaction and to understand the reactivity of the excited spin-orbit state of chlorine. The SEVI spectra are compared to simulations with and without non-adiabatic couplings between the Cl spin-orbit states. The non-adiabatic effects are found to be small but their inclusion improves agreement with experiment.

The second part of this work concerns the structure of ionic clusters which is studied with infrared multiple photon dissociation (IRMPD) spectroscopy. The stepwise solvation of the bicarbonate anion is probed by acquiring the IRPMD spectra of HCO₃^-(H₂O)_1-10 clusters in the gas-phase. Electronic structure calculations have been performed on the n=1-8 clusters to identify the structure of the low-lying isomers and to assign the observed spectral features. It is found that the water molecules preferably bind to the negatively charged CO₂ moiety of the HCO₃&hibar; anion. A binding motif consisting of a four-membered ring with each water forming a single H-bond with the CO2 moiety is found for clusters with n=4 or larger. In addition, the structure of the small (SiO)_3-5⁺ clusters have been studied with IRPMD and electronic structure calculations. The onset for the formation of the first Si-Si bond is observed for the n=5 cluster.