Photoelectron Spectroscopy of Organic Anions

Wren, Scott William

Graduate Thesis Or Dissertation

Photoelectron Spectroscopy of Organic Anions Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/gx41mh96x

Abstract

Wren, Scott William (Ph.D., Chemistry, Department of Chemistry and Biochemistry) Photoelectron Spectroscopy of Organic Anions Thesis directed by Professor W. Carl Lineberger Negative ion photoelectron spectroscopy is a very useful tool to investigate the properties of anions and their related neutral molecules. The neutral molecules that are formed when an electron is photodetached are often short-lived reactive radicals, which are difficult to study using other optical spectroscopy techniques. This thesis comprises several investigations that I performed on a series of related gas-phase anionic systems; these systems highlight the advantages and challenges associated with negative ion photoelectron spectroscopy. Additionally, a new innovative velocity mass filter was integrated into the existing instrument and its design and performance is described in detail.

The systems studied in this thesis can be coarsely divided into two classes of molecules. First, a series of six-membered aromatic rings are studied, where a nitrogen atom(s) is either inserted into the phenyl ring or is added as a substituent. Anilinide (C₆H₅NH^-) offers a straightforward example of a rigid molecular system having a simple photoelectron spectrum where all the spectral features are easily assigned. A series of five azinide anions (C_nH_nN_n^-) are then investigated to understand how the number of nitrogen atom(s) inserted into the phenyl ring and their position within the ring affect the thermochemical properties of the anion and neutral molecules. The photoelectron spectra of all five azinide anions have similar structure, though the measured electron affinities strongly depend on the proximity of the deprotonation site relative to the nitrogen atom(s).

The second class of molecules are anions which undergo drastic geometry changes when an electron is photodetached to form the neutral molecule. A series of halocarbene anions (CX₂- with X =Cl, Br, I) was investigated to definitively determine the energy difference between the ground state singlet and excited triplet state in the neutral carbene. The related dihalomethyl anions (CHX₂^-) are a much more challenging system to understand. The photoelectron spectra display an extended, structured vibrational progression due to the large geometry change between the anion and the neutral. A similar phenomenon is also found in the final two anions studied, c-C₄F₈- and SF₆^-, where high-level theoretical modeling is required to analyze the photoelectron spectra.

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