Photoelectron Spectroscopy of Solvated Electrons in Liquid Microjets By Alexander Truesdell ...

157 Pages·2012·6.28 MB·English

Photoelectron Spectroscopy of Solvated Electrons in Liquid Microjets
By
Alexander Truesdell Shreve

A dissertation submitted in partial satisfaction of the
Requirements for the degree of
Doctor of Philosophy
in
Chemistry
in the
Graduate Division
of the
University of California, Berkeley

Committee in charge:
Professor Daniel M. Neumark, Chair
Professor Evan R. Williams
Professor Robert Dibble
Fall 2012
Photoelectron Spectroscopy of Solvated Electrons in Liquid Microjets

Copyright © 2012
By
Alexander Truesdell Shreve
Abstract
Photoelectron Spectroscopy of Solvated Electrons in Liquid Microjets
By
Alexander Truesdell Shreve
Doctor of Philosophy in Chemistry
University of California, Berkeley
Professor Daniel M. Neumark, Chair

This dissertation presents studies of the binding energies of solvated
electrons in a variety of solutions. Solvated electrons play an important role
in radiation chemistry and biology, and have been the subject of many
studies since their discovery over a century ago. Information on their
binding energies, however, has been limited to the results of theoretical
calculations or inference from work with small solvent clusters. To directly
measure the solvated electron vertical binding energies (VBEs) in bulk
solution, a new apparatus was constructed coupling a liquid microjet source
to a photoelectron spectrometer. Using two photons from individual pulses of
a nanosecond laser, solvated electrons were generated and detached to
vacuum. Their kinetic energies were then measured with a field-free time-of-
flight spectrometer.
Studies are presented here that utilize this apparatus to measure the
VBEs of solvated electrons in water, methanol, ethanol, and acetonitrile.
Preliminary efforts to study solvated electrons in tetrahydrofuran are also
described. The findings of these studies are compared to past work on small
solvent clusters, doped with either an excess electron or an alkali metal
atom.
A second generation liquid microjet apparatus is also described. Using a
magnetic bottle time-of-flight spectrometer, the collection efficiency of the
next generation apparatus will be significantly higher than the original
apparatus.

1
Table of Contents
Abstract ........................................................................................ 1
Table of Contents .......................................................................... i
List of Figures .............................................................................. iii
List of Tables ............................................................................... vii
Acknowledgements .................................................................... viii
Chapter 1 Introduction ............................................................ 1
1.1 Overview .................................................................... 1
1.2 Bulk Solvated electrons ................................................ 1
1.3 Microsolvation in solvent clusters ................................... 2
1.4 Photoelectron spectroscopy ........................................... 5
1.4.1 Gas phase anions ............................................... 5
1.4.2 Gas phase neutrals ............................................. 6
1.4.3 Solvated electrons .............................................. 7
1.5 References .................................................................. 9
Chapter 2 Experimental Setup ............................................... 11
2.1 Overview .................................................................. 11
2.2 Principles of liquid microjets ........................................ 11
2.3 Practical application of microjets .................................. 14
2.4 Solvated electrons – generation and detachment ........... 18
2.5 Jets in vacuum – the microjet trap region ..................... 21
2.6 Field-free spectrometer – the detector region ................ 23
2.7 Data collection and processing .................................... 24
2.8 Calibration with anions ............................................... 25
2.9 Calibration with neutrals ............................................. 27
2.10 Streaming potentials .................................................. 29
2.11 Field-free collection efficiency ...................................... 32
2.12 Magnetic bottle spectrometer ...................................... 33
2.13 References ................................................................ 38
Chapter 3 Photoelectron Spectroscopy of Hydrated
Electrons................................................................ 39
3.1 Abstract ................................................................... 39
i
3.2 Introduction .............................................................. 39
3.3 Experiment ............................................................... 41
3.4 Results ..................................................................... 42
3.5 Discussion ................................................................ 43
3.6 Conclusions ............................................................... 45
3.7 Acknowledgements .................................................... 45
3.8 Figures ..................................................................... 46
3.9 References ................................................................ 50
Chapter 4 Photoelectron Spectroscopy of Solvated
Electrons in Alcohol and Acetonitrile Microjets ...... 53
4.1 Abstract ................................................................... 53
4.2 Introduction .............................................................. 53
4.3 Experimental ............................................................. 55
4.4 Results ..................................................................... 57
4.5 Discussion ................................................................ 58
4.6 Conclusions ............................................................... 61
4.7 Acknowledgements .................................................... 61
4.8 Figures and tables ..................................................... 62
4.9 References ................................................................ 66
Chapter 5 Photoelectron Spectroscopy of Solvated
Electrons in Tetrahydrofuran ................................. 69
5.1 Abstract ................................................................... 69
5.2 Introduction .............................................................. 69
5.3 Experimental ............................................................. 70
5.4 Preliminary results and discussion ................................ 71
5.5 Conclusions ............................................................... 75
5.6 Acknowledgements .................................................... 75
5.7 References ................................................................ 76
Appendix A Field-Free Spectrometer Machine Drawings ........... 77
Appendix B Magnetic Bottle Spectrometer Machine
Drawings ............................................................... 89
Appendix C Data Acquisition Software ................................... 131
C.1 From C++ to LabVIEW ............................................. 131
C.2 Non-time-resolved data collection program ................. 132
C.3 Time-resolved data collection program ....................... 134
C.4 References .............................................................. 137
Appendix D Data Processing Routines .................................... 139
D.1 Overview and purpose .............................................. 139
D.2 LabTalk script .......................................................... 139
ii
List of Figures
1.1 Anion cluster binding energy progressions .................................. 3
1.2 Comparison of anion and alkali doped cluster progressions ........... 4
2.1 Schematic overview of the apparatus ....................................... 12
2.2 Microjet nozzle ...................................................................... 15
2.3 Flowing microjet .................................................................... 16
2.4 Diffraction from a microjet ...................................................... 19
2.5 Detailed apparatus schematic ................................................. 20
2.6 Charge separation and velocity profile schematic ....................... 29
2.7 Streaming potential measurement scheme ............................... 30
2.8 Jet-walk energy shift ............................................................. 31
2.9 Calculation of the solid angle subtended by the detector ............ 32
2.10 Magnetic bottle photoelectron spectrometer .............................. 34
3.1 Schematic drawing of the spectrometer.................................... 46
3.2 Typical time-of-flight spectra of hydrated electrons .................... 47
3.3 Photoelectron spectra of hydrated electrons at 266 nm .............. 48
3.4 Photoelectron spectra of hydrated electrons at 213 nm .............. 49
4.1 Photoelectron spectra of solvated electrons in alcohol and
acetonitrile .......................................................................... 62
4.2 Vertical binding energy progressions of water, methanol,
and acetonitrile anion clusters ................................................ 63
5.1 Charging instability in tetrahydrofuran microjets ....................... 72
5.2 Streaming potential corrections in tetrahydrofuran
microjets ............................................................................. 73
iii
5.3 Preliminary photoelectron spectra of solvated electrons in
tetrahydrofuran .................................................................... 74
A.1 Jet trap region side view ........................................................ 78
A.2 Jet trap region top view ......................................................... 79
A.3 Mounting ring part 1 .............................................................. 80
A.4 Mounting ring part 2 .............................................................. 81
A.5 Differential pumping sheath .................................................... 82
A.6 Skimmer – 1 mm opening ...................................................... 83
A.7 Skimmer – 0.1 mm opening ................................................... 84
A.8 Jet trap top........................................................................... 85
A.9 Jet trap bottom ..................................................................... 86
A.10 Viewport entrance modification ............................................... 87
B.1 Full apparatus layout ............................................................. 90
B.2 Dewar cross detail ................................................................. 91
B.3 Jet cross detail 1 ................................................................... 92
B.4 Jet cross detail 2 ................................................................... 93
B.5 Detector cross detail .............................................................. 94
B.6 Liquid nitrogen dewar modification .......................................... 95
B.7 Detector support plate ........................................................... 96
B.8 Trap bottom ......................................................................... 97
B.9 Ice breaker ........................................................................... 98
B.10 Ice breaker feedthrough ......................................................... 99
B.11 Trap mount flange ............................................................... 100
B.12 Magnet platform post ........................................................... 101
B.13 Magnet support board .......................................................... 102
iv
B.14 Magnet baseplate ................................................................ 103
B.15 Iron cone ........................................................................... 104
B.16 Chamber door ..................................................................... 105
B.17 Differential pumping sheath .................................................. 106
B.18 Flight tube flange – full assembly .......................................... 107
B.19 Flight tube flange – outer tube components ............................ 108
B.20 Flight tube flange – outer tube .............................................. 109
B.21 Flight tube flange – inner tube components ............................ 110
B.22 Flight tube flange – inner tube .............................................. 111
B.23 Flight tube flange – connecting plate ...................................... 112
B.24 Flight tube in vacuum support ring ........................................ 113
B.25 Grid support post ................................................................ 114
B.26 Grid assembly mount ........................................................... 115
B.27 Grid ring bottom ................................................................. 116
B.28 Grid ring top ....................................................................... 117
B.29 Detector support rod ............................................................ 118
B.30 Detector mounting flange ..................................................... 119
B.31 Bottle assembly – full assembly ............................................ 120
B.32 Bottle assembly – wire support tube ...................................... 121
B.33 Bottle assembly – outer plastic tube ...................................... 122
B.34 Bottle assembly – mu metal shield ........................................ 123
B.35 Bottle assembly – retaining ring ............................................ 124
B.36 Bottle table stand bottom ..................................................... 125
B.37 Bottle table stand top .......................................................... 126
v
B.38 Flight tube table stand bottom .............................................. 127
B.39 Flight tube table stand top .................................................... 128
B.40 Dewar drying rest ................................................................ 129
B.41 Alternative grid mount ring ................................................... 130
C.1 GUI for the non-time-resolved data acquisition program .......... 132
C.2 GUI for the time-resolved data acquisition program ................. 135

vi
List of Tables
4.I Literature bulk excess electron binding energy values ................ 64
4.II Wavelength dependent signal levels in acetonitrile .................... 64
4.III Dielectric continuum calculation parameters ............................. 65

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