Photoelectron Spectroscopy of Organic Aromatic Anions

314 Pages·2017·8.18 MB·English

University of Colorado, Boulder
CU Scholar
Chemistry & Biochemistry Graduate Theses &
Chemistry & Biochemistry
Dissertations
Spring 1-1-2017
Photoelectron Spectroscopy of Organic Aromatic
Anions
Daniel John Nelson
University of Colorado at Boulder, [email protected]
Follow this and additional works at:https://scholar.colorado.edu/chem_gradetds
Part of thePhysical Chemistry Commons, and thePhysics Commons
Recommended Citation
Nelson, Daniel John, "Photoelectron Spectroscopy of Organic Aromatic Anions" (2017).Chemistry & Biochemistry Graduate Theses &
Dissertations. 235.
https://scholar.colorado.edu/chem_gradetds/235
This Dissertation is brought to you for free and open access by Chemistry & Biochemistry at CU Scholar. It has been accepted for inclusion in
Chemistry & Biochemistry Graduate Theses & Dissertations by an authorized administrator of CU Scholar. For more information, please contact
[email protected].
PHOTOELECTRON SPECTROSCOPY OF ORGANIC AROMATIC ANIONS

by
Daniel John Nelson
B.S., University of Wisconsin – Madison, 2010

A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
Chemical Physics
2017

i
This thesis entitled:
Photoelectron Spectroscopy of Organic Aromatic Anions
written by Daniel John Nelson
has been approved for the Committee on Chemical Physics
by

___________________________________
W. Carl Lineberger

___________________________________
Veronica M. Bierbaum

The final copy of this thesis has been examined by the signatories, and we
find that both the content and the form meet acceptable presentation standards
of scholarly work in the above mentioned discipline.

DATE:___________________

ii
Nelson, Daniel John (Ph.D. Chemical Physics)
Photoelectron Spectroscopy of Organic Aromatic Anions
Thesis directed by Professor W. Carl Lineberger
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 that is 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 group in the methylenephenoxides attracts
2
electron density from the oxygen site via resonance, as compared to the methylphenoxides. The
iii
singlet–triplet splittings 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.

iv
DEDICATION

To the memory of my late grandfather, whose name I bear, Daniel W. Nelson.

v
ACKNOWLEDGEMENTS
The simple truth is that there are far too many people to thank and acknowledge here who
have supported me throughout the sometimes grueling course of my graduate education. It was
only with the considerable compassion, love, and understanding of these people that I was able
to complete this Ph.D.
Of course, my advisor W. Carl Lineberger deserves special recognition. His advice and
counsel on both academics and life over the course of these last few years has been invaluable.
Carl, if you’re reading this, know that I will always treasure what you’ve taught me. In so many
ways, thank you.
Starting at the beginning of my graduate career, I must thank those people who took in an
arrogant, idiotic undergrad and transformed him into an experimentalist. Thank you to Joseph
Robert Roscioli, the post–doc who first trained me, starting from how to turn on a laser without
electrocuting myself. In a similar vein, I also thank David Nesbitt who opened my mind and
taught me, for the first time, how to actually understand quantum mechanics. Everyone in the
Nesbitt group at that time also deserves a thank you: Tom Baker, Andrej Grubisic, Grant
Buckingham, Mia Zutz, Nick Dupuis, Julie Fiore, Andy Gisler, Erik Holmstrom, Melanie
Roberts, and Mike Ziemkiewicz. After Rob left the group for new horizons, I would next work
with Monika Grütter Kasumaj, a phenomenal scientist I was privileged with the opportunity to
learn from.
I would subsequently begin my work in the Lineberger group, and specifically, I teamed
up with Wilson K. Gichuhi. Wilson and I would spend the next two years on one of the most
difficult projects I have ever been challenged with. Thank you so much for your patience and
tenacity, Wilson. I found in Wilson one of the kindest and most hard working people I will ever
vi
know. It was also at this time when I started to collaborate with the Bierbaum group, and
everyone there deserves my gratitude, including Charles Nichols, Callie Cole, and especially
Veronica M. Bierbaum, herself! Finally, the last post-doc I worked with was Julia H. Lehman.
Julia is, without question, one of the finest scientists I have ever met. Julia taught me how to be a
better scientist myself, and especially how to be a better writer. Julia would go on to become a
personal friend as well as professional colleague. Thank you, Julia. Your support and friendship
mean the world to me. In this last year of my studies I have worked with Allan Maple de
Oliveira, a fantastically enthusiastic grad student who has also become a friend of mine. Thank
you Allan, for your help and support- especially as I’ve slowly pulled a disappearing act these
last several months to try and actually complete this ridiculous document. Other members of the
Lineberger group deserve a thank you as well: Elisa M. Miller, Amanda Case, and Yu-Ju Lu.
All the members of the JILA support staff deserve my sincere thanks. You all are far
more talented and skilled than even your considerable reputation suggests. Terry Brown in the
electronics shop is especially deserving of my thanks. I had the pleasure of working extensively
with him to rebuild whole laser systems, and I couldn’t have asked for a better man to help in a
crisis.
Finally, I want to thank my friends and family. To my mom and dad, Jenny and Doug
Nelson, as well as my sisters, Katie Nelson Hardt and Sallie Nelson Haugen, thank you for all
the love and support you have given me my whole life. I wouldn’t be here without you. To my
old friends, Luke Justman, Nick Doremus, and Dylan Jambrek, thank you for keeping me mostly
sane through high school and undergrad. I love you guys. And to my new friends, Steve
Harshman, Tony Tumminello, Rashawn Griffin, and to the whole Magic club, you’ve all added
so much to my new life out here in Colorado. Thank you.
vii
CONTENTS

Chapter I: Introduction and Background
§ 1.1 Principles and Advantages of Anion Phototelectron Spectroscopy………………...1
§ 1.2 General Background on Aromatic Organic Molecules and Radicals………......….11
§ 1.3 Background on Methylphenoxides and Methylphenoxyls…………………...……15
§ 1.4 Background on Distonic Radical Anions and Diradicals:
Methylenephenoxides and Methylenephenoxyls……………………………..…18
§ 1.5 Background on Deprotonated Indole and Indoline……………………...………....21
§ 1.6 References……………………………………………………………………….…23

Chapter II: Experimental Background and Methods
§2.1 Introduction and Background………………………………………………………31
§2.2 Overview: Continuous Photoelectron Spectrometer………………………………..36
§2.3 Principles of Operation: Flowing–Afterglow Ion Source ……………….....………40
§2.4 Principles of Operation: Wien Velocity Filter……………………………………...44
§2.5 Principles of Operation: Argon–Ion Laser System…………………………………49
§2.6 Principles of Operation: Hemispherical Electron Energy Analyzer………………..68
§2.7 Overview: Pulsed Velocity Map Imaging Photoelectron Spectrometer……………73
§2.8 Principles of Operation: Dual Pulsed Valve Ion Source………………….......…….76
viii
§2.9 Principles of Operation: Wiley-McLaren Time-of-Flight Mass Spectrometer……..79
§ 2.10 Principles of Operation: Velocity Map Imaging Photoelectron Spectrometer...…81
§ 2.11 References……………………………………………….………………………..85
Chapter III: Anion Photoelectron Spectroscopy of Deprotonated o-, m-, and p-Methylphenol
§3.1 Introduction and Background……………………………………………………....87
§3.2 Experimental Specifics……………………………………………………………..89
§3.3 Theoretical Methods and Simulations……………………………………………...94
§3.4 Expectations and Error Analysis……………………………………………………96
§3.5 Electron Affinities and Term Energies……………………………………………..98
§3.6 Vibrational Analysis: ortho-Methylphenoxyl……………………………………..108
§3.7 Vibrational Analysis: meta-Methylphenoxyl……………………………………...115
§3.8 Vibrational Analysis: para-Methylphenoxyl……………………………………...120
§3.9 CH Deprotonated meta-Methylphenol…………………………………………...123
3
§3.10 Photon Energy Dependence of the para-Methylphenoxide Photoelectron Spectra
…………………………………………………………………………………………..127
§3.11 Discussion………………………………………………………………………..133
§ 3.12 Conclusions……………………………………………………………………...139
§3.13 References………………………………………………………………………..140
ix