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Anion Photoelectron Spectroscopy

TitleAnion Photoelectron Spectroscopy
Publication TypeThesis
Year of Publication2006
AuthorsAndrews, DH

This thesis presents the results of anion photoelectron spectroscopy experiments conducted on three classes of anions. One class is that of heteronuclear coinage metal diatomic molecules. These include AgO−, AuO−, AuS−, CuH−, and CuD−. The photoelectron spectra of these molecules are characterized by short vibrational progressions in transitions to the ground electronic states and confident assignments of the electronic state origins and electron affinities. The photoelectron spectra of these molecules measured for the first time the electron affinities of the corresponding neutral molecules. Frank-Condon simulation of the observed ground state vibrational structure coupled with observation of a well characterized excited state allowed for the assignment of the anion equilibrium bond lengths for AgO−, CuH−, and CuD−. Because no excited electronic states were observed in the photoelectron spectra of AuO− and AuS−, only the magnitude of the bond length change between the anion and the neutral molecules was assigned. Observation of hot-bands in the photoelectron spectra allowed for the first assignment of anion harmonic vibrational frequencies for AgO− and AuS−. In addition, a predicted, yet previously unobserved, 3Σ+ excited electronic state of CuD and CuH was observed in the photoelectron spectra of CuD− and CuH−.

The second class of molecules studied was that of copper anion complexes. These included Cu−CD3OD, CuCD3O−, CuH2−, and CuD2−. The photoelectron spectra of these complexes are characterized by extended vibrational progressions in the transitions to nearly all observed electronic states. These extended vibrational progressions are the product of large geometry changes between the anion and neutral complexes. The geometry change between the anion and neutral of CuH2 and CuD2 is also very severe, as the anions are linear and the neutrals are bent. The spectra are dominated by a short vibrational progression in the symmetric stretch mode which allows determination of the electron affinities of CuH2 and CuD2.

The photoelectron spectra of two related organic compounds were also taken. Photoelectron spectra of the 1,2,3-triazolide anion were recorded and show signatures of strong vibronic coupling of the low lying electronic states of the neutral. Still, the vibrational origin of transitions to the ground electronic state of the neutral allowed for easy assignment of the neutral electron affinity. Combination of the measured electron affinity with the gas phase acidity measured elsewhere allowed for determination of the N-H bond dissociation energy of the parent molecule 1H-1,2,3-triazolide. In addition, the heat of formation of the 1,2,3-trizolyl radical was also determined. It was also found that, under the experimental source conditions used in these experiments, about 40% of the 1,2,3-triazolide anions ring open to form the E-iminodiazomethide anion, the structure of which was assigned on the basis of a simulation of the measured photoelectron spectrum. The simulation also allowed assignment of several normal mode frequencies of the anion and neutral.