This thesis entitled:
Temperature Dependent Rate Constant for the OH + O
3
Chain Reaction via High
Resolution Infrared Laser Absorption Methods
written by Bradley W. Blackmon
has been approved for the Department of Chemistry
_____________________________
David J. Nesbitt
_____________________________
Veronica Vaida
Date_____________
The final copy of this thesis has been examined by the
signators, and we find that both the content and the form
meet acceptable presentation standards of scholarly work in
the above mentioned discipline. iii
Blackmon, Bradley Wayne (M.S., Chemistry)
Temperature Dependent Rate Constant for the OH + O
3
Chain Reaction via High
Resolution Infrared Laser Absorption Methods
Theis directed by Professor David J. Nesbitt
The goal of this work is to determine the rate constant of the catalytic chain
reaction of hydroxyl radical (OH) with ozone (O
3
). This chain reaction proceeds in
two steps: (1) OH + O
3
HO
2
+ O
2
, with rate constant k
1
, and (2) HO
2
+ O
3
OH + 2 O
2
, with rate constant k
2
. These rate constants are determined by observing
the temporal profile of OH radical via direct infrared absorption, and fitting the data
to a model consistent with the exact solution for the entire chain reaction process.
The technique of direct infrared absorption allows us to probe the kinetics over an
order of magnitude greater dynamic range of ozone concentration than previous
studies, which provides clearer separation between the chain induction (k
ind
= k
1
+
k
2
), propagation, and termination steps. By utilizing a temperature-controlled flow
tube, we are able to extract the temperature dependence of the kinetics as well. The
Arrhenius form for k
ind
= k
1
+ k
2
between 334 and 240K is determined to be
(
)




± ×
=



+

)
K
(
K
)
50
1030
(
exp
10
93
.
2
sec
cm
)
(
12
42
.
0
38
.
0
3
ind
T
T
k
. This value is
significantly higher than the values currently recommended for use in atmospheric
models. Kinetic analysis of k
ind
below 240K and the ratio of k
2
/k
ind
have also been
investigated. To All My Teachers in Life ACKNOWLEDGEMENTS
There are many people who have made this thesis, and this work, possible.
First, and foremost, I would like to thank my wife, Ida, for giving me the strength
and courage to look within myself and find that which truly makes me happy.
Thank you for your encouragement and support during this very hectic time. She
has made me realize what is really important, and has shown me the magic inherent
in life.
I would also like to thank the very many people with whom I have had the
honor of working. Thanks to Bill Chapman, for his support and encouragement,
both in the lab and out. I would also like to thank Sergey Nizkorodov, for all his
hard work fitting the mountains of data; Scott Davis, for all the lunch-time
conversations; and Tyson Nunemacher, for showing me how to brew the best pale
ale Ive ever tasted. Thank you to everyone else who made my stay here much
more bearable: Ondrej Votava, Joanna Fair, David Charlie Anderson, Dairene Uy,
Nikki Delaney, Tanya Meyers, Stuart Macenzie, Joe Kim, Hendrik Hamann, and
Barb Tennis, I would also like to thank my parents and brother: Gary, Kathy, and
Ryan, for their constant love and support.
Finally, I would like to thank my advisor, David Nesbitt, for teaching me to
be a truth seeker, and whose dedication and determination will always keep me in
awe. CONTENTS
CHAPTER
1.

INTRODUCTION .......................................................................1
2.

EXPERIMENTAL.......................................................................9
2.1

Introduction...........................................................................9
2.2

Experimental Apparatus .......................................................10
2.3

The Temperature Controlled Flow Cell................................19
2.4

The Questek Excimer Laser..................................................21
2.5

The Kr Ion Laser...................................................................22
3.

DATA AND RESULTS ..............................................................28
3.1

Kinetic Analysis....................................................................28
3.2

Room Temperature Results ..................................................35
3.3

Systematic Checks ................................................................40
3.4

Temperature Dependent Results ...........................................42
3.5

k
2
/k
ind
Determination at Room Temperature.........................46
3.6

Breaking the 240 K Barrier...................................................48
3.7

Conclusion ............................................................................51
4.

F+H
2
REACTIVE SCATTERING ..............................................55
4.1

Introduction...........................................................................55 vii
4.2

Experiment............................................................................57
4.3

Results and Analysis .............................................................60
4.4

Comparison with Theory ......................................................62
BIBLIOGRAPHY..........................................................................................67
APPENDIX
A.

PROGRAMMING THE DSP TRANSIENT
DIGITIZER/AVERAGING MEMORY................................72
A.1 Reading Parameters From the DSP ......................................74
A.2 Writing Parameters to the DSP ............................................78
A.3 Block Transfer......................................................................81
A.4 Setting Up the Digitizer/Averaging Memory.......................82
A.5 Using the Digitizer/Averaging Memory...............................85
A.6 The Scanner 1.0 Program .....................................................86 viii
TABLES
Table
2.1

The Temperature Dependent Cross Section and
Quantum Yield for Ozone at 308 nm.........................19
2.2

Freezing Point for Various Fluids Used to Cool the
Flow Cell....................................................................21
2.3

Kr Ion Laser Tube Voltage at Various Tap Positions............23
3.1

Reactions Occurring in the flow cell and their
respective rate constants ............................................35
3.2

Experimental Conditions for the Room Temperature
Determination of k
ind
..................................................36
3.3

Room Temperature Values for k
ind
........................................39
3.4

Typical Conditions and k
ind
at Various
Temperatures .............................................................43
3.5

Comparison of k
ind
with Previously Determined
Values ........................................................................45
3.6

Typical Conditions and k
ind
at Temperatures below
240 K..........................................................................50
A.1
Pin Assignments for the 2001AS 4101 Interface................73
A.2
The ASCII Character Set .......................................................76
A.3
Data Types and Sizes .............................................................80
A.4
Bit Positions for the Setup Parameters for the
2001AS ......................................................................83 FIGURES
Figure
1.1
Ozone Density as a Function of Altitude...............................2
1.2
Atmospheric Temperature as a Function of Altitude.............4
2.1
Experimental Setup................................................................10
2.2
OH/HO
2
/O
3
Chain Reaction Scheme.....................................11
2.3
Temperature Controlled Flow Cell ........................................13
2.4
IR Detection Noise Spectrum ................................................14
2.5
The Gas Handling System .....................................................15
2.6
Vapor Pressure of Water as a Function of
Temperature ...............................................................16
2.7
Temperature Dependence of the Ozone Cross
Section .......................................................................18
2.8
Block Diagram of the Kr Ion Laser .......................................23
2.9
Varian 801 Meter Calibration ................................................24
2.10
Test Circuit for the Kr Ion laser Power Transistor
Banks .........................................................................25
3.1
OH Radical Rise Time Profiles .............................................30
3.2
Typical OH Absorbance Data................................................32
3.3
Stern-Volmer Analysis at 298 K............................................38 x
3.4
Room Temperature Rate Constant as a Function of
Excimer Laser Energy................................................40
3.5
Room Temperature Rate Constant as a Function of
Buffer Gas Pressure ...................................................42
3.6
Stern-Volmer Analysis at Various Temperatures ..................43
3.7
Arrhenius Plot for the Induction Decay Rate.........................45
3.8
k
2
/k
ind
Determination at 298 K ...............................................47
3.9
Typical OH Absorbance Data with H
2
as the Sole
Precursor ....................................................................49
3.10
Arrhenius Plot Including Data below 240 K .........................50
4.1
Schematic Diagram of the Crossed Jet Direct
Absorption Reactive Scattering Experiment..............58
4.2
Sample Absorption Signals from the HF(v=3)
produced by Reactive Scattering of F atoms
w