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Photoelectron Spectroscopy of Organic Aromatic Anions

Event Details

Event Dates: 

Friday, August 18, 2017 - 3:00pm

Seminar Location: 

  • JILA X317

Speaker Name(s): 

Dan Nelson

Speaker Affiliation(s): 

CU Boulder
Seminar Type/Subject

Scientific Seminar Type: 

  • JILA Thesis Defense

Event Details & Abstract: 

This dissertation reports and interprets the results of experiments in which photoelectron spectroscopy was performed on a variety of aromatic anions. In addition to these photoelectron studies, the results and conclusions of an experiment in which HCl is scattered off atomically flat Au (111) surfaces are also presented.

     Photoelectron spectroscopy of the isomers of methylphenoxide reveals that these molecules display minimal vibrational excitation upon photodetachment, accessing the electronic ground and first excited state of the corresponding radicals. The photoelectron spectra of /p-/methylphenoxide reveal a photon energy dependence arising from electron autodetachment. The slow electron velocity map imaging (SEVI) technique was employed to obtain the electron affinities (EAs) of these radicals with an uncertainty of 1.4 meV. Combining the measured EAs with previously measured O–H bond dissociation energies in a thermodynamic cycle allows for the measurement of the acidities of the methylphenols with an uncertainty an order of magnitude smaller than any previous measurement.

     The full interpretation of the photoelectron spectra of the isomers of methylenephenoxide presents a far greater challenge with many subtleties. The EAs of/o-/ and /p-/methylenephenoxyl were measured and shown to be ~1 eV lower in energy than for the methylphenoxyls, implying that the electron withdrawing effect of the CH_2 group in the methylenephenoxides attracts electron density from the oxygen site via resonance, as compared to the methylphenoxides. The singlet–triplet splitting of the diradicals /o-/ and/p-/methylenephenoxyl were measured. The acidities of the methylenephenols were measured by acid bracketing. Combining the EAs of the methylenephenoxyls with these acidities allows for a measurement of the weak O-H bond dissociation energy of the methylenephenols.

The photoelectron spectra of indolide were obtained and interpreted. The structure of indolide minimally distorts upon electron photodetachment accessing the electronic ground doublet state of indolyl. The EA of indolyl was measured utilizing the SEVI technique with an uncertainty of 1.7 meV. Ring distortion vibrational modes were found to be excited upon electron photodetachment. The previously measured acidity of indole is combined with our measurement of the EA of indolyl to determine the N–H bond dissociation energy of indole.