Zero Kinetic Energy Photoelectron Spectroscopy of Polycyclic Aromatic Hydrocarbons

202 Pages·2015·7.18 MB·English

by  Harthcock, Colin

AN ABSTRACT OF THE DISSERTATION OF
Colin Harthcock for the degree of Doctor of Philosophy in Chemistry, presented on
December 4, 2015
Title: Zero Kinetic Energy Photoelectron Spectroscopy of Polycyclic Aromatic
Hydrocarbons.

Abstract approved:
_____________________________________________________________
Wei Kong

In this dissertation, I describe spectroscopic studies of jet-cooled polycyclic
aromatic hydrocarbons (PAH) and one nitrogen substituted PAH (PANH) using pulsed
field zero kinetic energy (ZEKE) photoelectron spectroscopy and resonantly enhanced
multiphoton ionization (REMPI) spectroscopy. Recently, there has been a demand for
far-infrared (FIR) spectral information of astrophysically relevant molecules by the
National Aeronautics and Space Administration (NASA). Concurrent with the launching
of the Herschel Space Observatory and the Stratospheric Observatory for Infrared
Astronomy (SOFIA), NASA is on a mission to map out the chemical composition of the
interstellar medium. In response to this call and in answering a broader interest in
modeling the energy balance of the astrophysical environment, we have initiated a
systematic study of polycyclic aromatic hydrocarbons, concentrating on the vibrational
information in the FIR for the first electronically excited state and for the ground
electronic state of the cation. From the REMPI experiment, we have learned that the
vibronic structure of small stable PAHs generally follows the Franck-Condon principle,
but vibronic coupling is prevalent for most larger sized PAHs. Nitrogen substitution can
affect the nature of the electronic states and hence the vibronic distribution of the REMPI
spectrum and ultimately the ZEKE spectra. Different from REMPI, ZEKE spectra
typically follow the Franck-Condon principle, and spectral simulations using the
Gaussian software package can typically reproduce the ZEKE spectrum obtained from
the origin of the electronic transition qualitatively. Although ZEKE does not offer
direction infrared transition intensities, our spectroscopic information in the FIR can
benchmark theoretical values and offer guidance for NASA’s astrophysical missions.
© Copyright by Colin Harthcock
December 4, 2015
All Rights Reserved
Zero Kinetic Energy Photoelectron Spectroscopy
of Polycyclic Aromatic Hydrocarbons

by
Colin Harthcock

A DISSERTATION
submitted to
Oregon State University

in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy

Presented December 4, 2015
Commencement June 2016
Doctor of Philosophy dissertation of Colin Harthcock presented on December 4, 2015
APPROVED:

Major Professor, representing Chemistry

Chair of the Department of Chemistry

Dean of the Graduate School

I understand that my dissertation will become part of the permanent collection of Oregon
State University Libraries. My signature below authorizes release of me dissertation to
any reader upon request.

Colin Harthcock, Author
ACKNOWLEDGEMENTS
After years of studious diligence; hours and hours spent in labs and tests, I am
finally nearing my goal of earning a doctorate in chemistry. I know that my dream of a
PhD in chemistry would not have been possible without the help of many people.
First, I would like to thank Dr. Chuck Williamson who first introduced me to the
world of chemistry and laboratory research. Secondly, thank you Wei for the chance to be
here at Oregon State University so that I can pursue my dream under her careful tutelage.
Her availability and willingness to answer any question was and is extraordinary. I am
forever in her debt. From the moment that I took my first step into the lab, Jie took me
under her wing, going above and beyond to ensure that I knew everything when I took
over her research.
I would also like to take a moment to acknowledge my lab mates, who have
always been there to lend a helping hand when I needed it. Specifically I would like to
thank Bill Freund who was always a fount of knowledge for all things electronic as well
as Mark Warner, whose assistance proved invaluable. I would also like to thank the
countless others at the university who helped me along the way.
My deepest appreciation goes out to my doctoral committee; Dr. Evans, Dr.
Watson, Dr. Ostroverkhova, Dr. Strub, and Dr. McIntyre whose direction has been
tremendously helpful.
Last but defiantly not least, I would like to express my most heartfelt thanks for
my parents, whose unwavering support has helped me though the good and bad times.
TABLE OF CONTENTS
Page
Chapter 1. Introduction ........................................................................................................1
1.1 Background - Why PAH and PANH? ...............................................................1
1.2 History and principle of ZEKE spectroscopy ....................................................4
1.3 Summary ............................................................................................................8
1.4 References ..........................................................................................................9
Chapter 2. Experimental Setup ..........................................................................................13
2.1 General description ..........................................................................................13
2.2 Laser systems ...................................................................................................15
2.3 Sample source ..................................................................................................17
2.4 Spectrometer ....................................................................................................19
2.5 Timing ..............................................................................................................22
2.6 Typical experimental procedure ......................................................................23
2.7 Gaussian calculations .......................................................................................26
2.8 References ........................................................................................................26
Chapter 3. Zero kinetic energy photoelectron spectroscopy of triphenylene ....................27
3.1 Introduction ......................................................................................................29
3.2 Experimental setup and calculation method ....................................................30
3.3 Results ..............................................................................................................32
3.4 Discussions ......................................................................................................47
3.5 Conclusions ......................................................................................................52
3.6 References ........................................................................................................53
Chapter 4. Resonantly enhanced multiphoton ionization and zero kinetic energy
photoelectron spectroscopy of chrysene: A comparison with tetracene ...........57
TABLE OF CONTENTS (Continued)
Page
4.1 Introduction ......................................................................................................59
4.2 Experimental ....................................................................................................61
4.3 Results ..............................................................................................................61
4.4 Discussion ........................................................................................................71
4.5 Conclusion .......................................................................................................80
4.6 References ........................................................................................................81
Chapter 5. Zero Kinetic Energy Photoelectron Spectroscopy of benzo[h]quinoline .........85
5.1 Introduction ......................................................................................................87
5.2 Experimental Setup and Calculation Method ..................................................89
5.3 Results ..............................................................................................................91
5.4 Discussion ......................................................................................................101
5.5 Conclusion .....................................................................................................106
5.6 References ......................................................................................................107
Chapter 6. Resonantly enhanced multiphoton ionization and zero kinetic energy
photoelectron spectroscopy of benzo[e]pyrene ...............................................112
6.1 Introduction ....................................................................................................114
6.2 Experimental setup.........................................................................................115
6.3 Results ............................................................................................................116
6.4 ZEKE Spectroscopy .......................................................................................122
6.5 Discussions ....................................................................................................127
6.6 Conclusions ....................................................................................................131
6.7 References ......................................................................................................132
Chapter 7. Zero Kinetic Energy Photoelectron spectroscopy of jet cooled benzo[a]pyrene
from resonantly enhanced multiphoton ionization ..........................................134
TABLE OF CONTENTS (Continued)
Page
7.1 Introduction ....................................................................................................136
7.2 Experimental setup.........................................................................................139
7.3 Results ............................................................................................................140
7.4 Discussion ......................................................................................................153
7.5 Conclusion .....................................................................................................159
7.6 References ......................................................................................................160
Chapter 8. Resonantly enhanced multiphoton ionization and zero kinetic energy
photoelectron spectroscopy of benzo[g,h,i]perylene .......................................163
8.1 Introduction ....................................................................................................165
8.2 Experimental setup.........................................................................................167
8.3 Results ............................................................................................................168
8.4 ZEKE spectroscopy .......................................................................................173
8.5 Discussion ......................................................................................................180
8.6 Conclusion .....................................................................................................183
8.7 References ......................................................................................................184
Chapter 9. Concluding Remarks ......................................................................................186
9.1 General Implications ......................................................................................186
9.2 Extreme vibronic coupling in triphenylene ....................................................188
9.3 Effect of nitrogen substitution in PANHs ......................................................189
9.4 References ......................................................................................................189
LIST OF FIGURES
Figure Page
1.1 The PAH and PANH molecules included in this thesis .................................................2
2.1 Overall experimental setup and signal processing .......................................................14
2.2 Details of the vacuum system ......................................................................................15
2.3 Details of the heatable pulse valve ...............................................................................18
2.4 Details of the electrodes, TOF and sample source .......................................................19
2.5 The MCP detection circuit employed for the detection of cations and electrons ........20
2.6 Relative timings for the PFI-ZEKE experiment ..........................................................23
3.1 REMPI spectrum of triphenylene ................................................................................33
3.2 Comparison between the experimental REMPI and simulation ..................................36
3.3 Experimental ZEKE spectra ........................................................................................39
3.4 Experimental ZEKE spectra ........................................................................................40
3.5 The 1e’ vibrational mode of S (D ) and its resolution into the modes of D (C ) ...46
1 3h 0 2v
4.1 REMPI spectrum of jet-cooled chrysene .....................................................................62
4.2 ZEKE spectra of chrysene ...........................................................................................66
4.3 Comparison between experimental and simulated ZEKE spectra ...............................69
4.4 Calculated molecular orbitals of chrysene ...................................................................72
4.5 REMPI and ZEKE spectra of tetracene from the origin band of the REMPI spectrum79
5.1 REMPI spectrum of benzo[h]quinoline .......................................................................92
5.2 Comparison between the experimental REMPI spectrum and simulation using DFT 93
5.3 Experimental ZEKE spectra of benzo[h]quinoline ......................................................99
6.1 REMPI spectrum of benzo[e]pyrene .........................................................................117
6.2 Comparison between REMPI and DFT simulations ..................................................120
6.3 ZEKE spectra of BeP .................................................................................................125
LIST OF FIGURES (Continued)
Figure Page
6.4 ZEKE spectra of BeP .................................................................................................126
7.1 Structure of benzo[a]pyrene and coordinate system ..................................................138
7.2 REMPI spectrum of benzo[a]pyrene .........................................................................141
7.3 Comparison between REMPI and DFT simulations ..................................................145
7.4 ZEKE spectra of BaP .................................................................................................151
7.5 ZEKE spectra of BaP .................................................................................................152
7.6 Comparison between ZEKE origin and DFT simulation ...........................................157
8.1 REMPI spectrum of jet-cooled benzo[g,h,i]perylene ................................................169
8.2 Simulation of the BghiP excitation spectra ................................................................172
8.3 ZEKE spectra of BghiP ..............................................................................................178
8.4 ZEKE spectra of BghiP ..............................................................................................179
8.5 DFT simulation of the ZEKE spectrum collected via the REMPI origin ..................180