SPECTROSCOPIC STUDY OF METHANE IN THE + BAND BROADENED BY ITSELF, AIR AND HYDROGEN MD ARIFUZZAMAN Master of Science, Shah Jalal University of Science and Technology, 2009 A Thesis Submitted to the School of Graduate Studies of the University of Lethbridge in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE Department of Physics and Astronomy University of Lethbridge LETHBRIDGE, ALBERTA, CANADA © Md Arifuzzaman, 2018 SPECTROSCOPIC STUDY OF METHANE IN THE + BAND BROADENED BY ITSELF, AIR AND HYDROGEN MD ARIFUZZAMAN Date of defence: April 27, 2018 Dr. M. Gerken Professor Ph.D. Thesis Supervisor Dr. B. Billinghurst Adjunct Assistant Professor Ph.D. Thesis Examination Committee Member Senior Scientist, Canadian Light Source. Inc. Saskatoon Dr. B. Seyed-Mahmoud Associate Professor Ph.D. Thesis Examination Committee Member Dr. A. Cross Adjunct Assistant Professor Ph.D. Thesis Examination Committee Member Dr. G. Tabisz Professor and Senior Scholar Ph.D. External Examiner Department of Physics and Astronomy University of Manitoba, Canada Dr. D. Naylor Professor Ph.D. Chair, Thesis Examination Committee Dedication This thesis is dedicated to my beloved parents, my wife and my daughter. iii Abstract This thesis presents the temperature-dependent line-shape studies of methane broadened by itself, air and hydrogen, which is identified as the second most important anthropogenic greenhouse gas in the Earth’s atmosphere due to its high global warming potential. A set of 14 laboratory spectra of pure methane and lean mixtures of methane in air were recorded over a range of temperatures from 148.4 to 298.4 K and total sample pressures from 4.5 to 385 Torr using a high-resolution Fourier Transform Spectrometer (FTS) at the Jet Propulsion Laboratory (JPL), California. A coolable absorption gas cell with the optical path length 20.38 cm was used in the recording of methane-air spectra. A non-linear least-squares multi-spectrum fitting program called ‘Labfit’ was used to determine the Lorentz half-width, pressure-induced shift coefficients along with their temperature dependences, speed-dependence parameters and line-mixing coefficients due to self- and air-broadening of methane in its strongest band + . A set of 18 laboratory spectra of methane broadened by itself and hydrogen were also recorded at various temperatures (148.4-298.4 K) and pressures (0.12-385 Torr) using an FTS at JPL. Various line-shape parameters such as line positions, intensities, self- and air-broadened line widths and pressure-induced shifts along with their temperature dependences are reported in the + band of methane. A Speed-Dependent Voigt Profile (SDVP) was implemented in the retrieval of line parameters in both cases. The line- mixing coefficients were quantified using the off-diagonal relaxation matrix element formalism. The off-diagonal relaxation-matrix coefficients were determined due to self-, air- and H2-broadening of methane using Labfit program. iv Acknowledgements All praises is due to almighty God for whom I am here in this world to do these types of research works and I pray Him to accept this as the good deed. First and foremost, I am deeply thankful to my supervisor, Dr. Michael Gerken, Professor, Department of Chemistry and Biochemistry for his continuous supports and important guidelines throughout my M.Sc. program. I found him very cordial, prompt and helpful. He is an enthusiastic leader in the field of research, from whom I had the privilege of learning not only research work but also the way to be responsible in everyday life. His motivation and guidance helped me to continue and accomplish my thesis works. I would like to pay special thanks to my previous supervisor, Dr. Adriana Predoi- Cross, who accepted me as a graduate student in her research group. I gained useful knowledge from her about fitting and analyzing spectroscopic data using ‘Labfit’. I would like to express my gratitude to all of my committee members, Dr. Behnam Seyed Mahmoud, Dr. Albert Cross and Dr. Brant Billinghurst for their important guidelines and suggestions to make an executable research plan during my graduate studies. I am thankful to Dr. Chad Povery, instructor, Physics and Astronomy at University of Lethbridge, who is also an alumnus as a Ph.D. student in our research group. I discussed many research questions with him and I found him very knowledgeable and helpful. I am grateful to Dr. Keeyoon Sung, scientist at Jet Propulsion Laboratory (JPL), Caltech, who provided me the experimental data for the analysis. I also communicated with him about the fitting procedures and he responded to me very quickly. I am also thankful v to Dr. Malathy Devi, Reseacrh Professor at the College of William and Mary, who provided me useful guidelines about fitting procedures using ‘Labfit’ especially for line-mixing calculations. Dr. Chris Benner at the College of William and Mary is thanked for allowing me to use his multi-spectrum fitting software “Labfit”. The contribution of Dr. Arlan Mantz from Department of Physics, Geophysics and Astronomy, Connecticut College is highly acknowledged for designing the cryogenic type gas cell, which was used in the recording of my spectra at JPL. I am very thankful to all of my colleagues and fellows in the Department of Physics and Astronomy, especially to Hoimonti Rozario, Ph.D. student, Robab Hashemi, Ph.D student, Md Kamruzzaman, Ph.D. student, Abdullah Al Mashwood and Nazrul Islam, alumni in our research group. Last but not least, I would like to pay special thanks to my parents, my beloved daughter Rubaba Afsheen and my wife Rabeya Parvin, because of their unconditional supports along with patience towards the completion of my graduate studies. Finally, I am grateful to the center of excellence in research of School of Graduate Studies at University of Lethbridge supported by Natural Sciences and Engineering Research Council of Canada (NSERC) and the NSERC-supported AMETHYST program. vi Table of Contents Dedication ...................................................................................................................... iii Abstract .......................................................................................................................... iv Acknowledgements ......................................................................................................... v CHAPTER 1: INTRODUCTION .................................................................................... 1 1.1 Overview ............................................................................................................... 1 1.2 General information of methane ............................................................................. 2 1.3 Methane as a greenhouse gas .................................................................................. 2 1.4 Methane contribution to carbon cycle ..................................................................... 3 1.5 Methane as a constituent of exoplanetary atmosphere ............................................. 4 1.6 Motivation of methane line-shape studies ............................................................... 4 1.7 Summary of previous methane line-shape studies ................................................... 6 1.8 Goal and objectives of my present research .......................................................... 10 CHAPTER 2: THEORETICAL CONCEPTS ................................................................ 12 2.1 Quantum mechanical aspects of energy ................................................................ 12 2.1.1 History of quantum mechanics ....................................................................... 12 2.1.2 Rotational energy of a simple diatomic molecule ........................................... 13 2.1.3 The expression of vibrational energy of a simple diatomic molecule .............. 14 2.1.4 Interaction of electromagnetic radiation with matter ....................................... 16 2.2 Rotation-vibration spectroscopy ........................................................................... 19 2.2.1 Pure rotation .................................................................................................. 19 2.2.2 Rotational spectra .......................................................................................... 20 2.2.3 Transition intensity ........................................................................................ 22 2.2.4 Centrifugal distortion ..................................................................................... 23 2.3 Vibrational spectroscopy ...................................................................................... 24 2.3.1 Vibrational energy of a diatomic molecule ..................................................... 25 2.3.2 Infrared spectra of a diatomic molecule .......................................................... 25 2.3.3 Vibrational energy of a non-linear polyatomic molecule ................................ 29 2.4 Rotation-vibration spectroscopy ........................................................................... 30 2.4.1 Infrared spectra of methane ............................................................................ 32 2.5 Theory of line-shapes ........................................................................................... 35 2.5.1 Natural line broadening-Lorentzian line-shape ............................................... 36 2.5.2 Doppler broadening-Gaussian line-shape.......................................................