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Ab Initio Quantum Chemical Studies on Neutral Florida International University FIU Digital Commons FIU Electronic Theses and Dissertations University Graduate School 11-2-2012 Ab Initio Quantum Chemical Studies on Neutral- Radical Reactions of Ethynyl (C2H) and Cyano (CN) with Unsaturated Hydrocarbons Adeel Jamal Florida International University, [email protected] DOI: 10.25148/etd.FI12111903 Follow this and additional works at: https://digitalcommons.fiu.edu/etd Recommended Citation Jamal, Adeel, "Ab Initio Quantum Chemical Studies on Neutral-Radical Reactions of Ethynyl (C2H) and Cyano (CN) with Unsaturated Hydrocarbons" (2012). FIU Electronic Theses and Dissertations. 736. https://digitalcommons.fiu.edu/etd/736 This work is brought to you for free and open access by the University Graduate School at FIU Digital Commons. It has been accepted for inclusion in FIU Electronic Theses and Dissertations by an authorized administrator of FIU Digital Commons. For more information, please contact [email protected]. FLORIDA INTERNATIONAL UNIVERSITY Miami, Florida AB INITIO QUANTUM CHEMICAL STUDIES ON NEUTRAL-RADICAL REACTIONS OF ETHYNYL (C2H) AND CYANO (CN) WITH UNSATURATED HYDROCARBONS A dissertation in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in CHEMISTRY by Adeel Jamal 2012 To: Dean Kenneth Furton choose the name of dean of your college/school College of Arts and Sciences choose the name of your college/school This dissertation, written by Adeel Jamal and entitled Ab Initio Quantum Chemical Studies on Neutral-Radical Reactions of Ethynyl (C2H) and Cyano (CN) with Unsaturated Hydrocarbons, having been approved in respect to style and intellectual content, is referred to you for judgment. We have read this dissertation and recommend that it be approved. _______________________________________ Jeffrey Joens _______________________________________ David Chatfield _______________________________________ Yong Cai _______________________________________ John Zweibel _______________________________________ Alexander Mebel, Major Professor Date of Defense: November 2, 2012 The dissertation by Adeel Jamal is approved. _______________________________________ choose the name of dean of your college/school Dean Kenneth Furton choose the name of your college/school College of Arts and Sciences _______________________________________ Dean Lakshmi N. Reddi University Graduate School Florida International University, 2012 ii © Copyright 2012 by Adeel Jamal All rights reserved. iii DEDICATION This work is dedicated to the three women in my life; my mother, Farida Jamal, my sister, Rabiya Jamal, and my grandmother, Zubaida Jamal. They were encouraging when times were good and supportive when times were tough. I strive to excel in life because they strived in excelling me in life. And in loving memory of my late father, Mohammed Jamal, and my late brother, Umer Jamal. iv ACKNOWLEDGMENTS First and foremost, I would like to thank Alexander Mebel, my major professor, for being a mentor, friend, and an inspiration. It was his aid that paved my way through the Doctor of Philosophy process, both from a professional and personal level. He is the reason why I chose theoretical chemistry. I only hope to be a mentor of future scientists the way he was a mentor to me. A big consideration goes out to my committee members. Dr. Jeff Joens was instrumental in my understanding of physical and quantum chemistry. His style of teaching was very conversational and his ability to reflect abstract concepts using mathematics was refreshing. Dr. David Chatfield has been a part of my memories since I first entered college. His style of teaching made me admire and respect the value of chemistry. Dr. Yong Cai was the graduate director and was integral during the commencement of my graduate studies. Finally, Dr. John Zweibel has been approachable and receptive, despite having the disfamiliarity with the chemical sciences, and his enthusiasm towards quantum chemistry was well appreciated . Last, but certainly not least, my family and friends for sticking through all these years and being supportive. I couldn’t have done this without your love and compassion To Reby Valdi, who has been by my side during much of my graduate studies. A big consideration goes out to my colleagues during my graduate studies, especially Alexander Lander and Armando Pardillo. Our conversations could never get dull as long as we have science to discuss. Nash Naviwala, for being a brother and an uncle. He always believed I can accomplish anything as long as I pursue it. And finally, Jeff West v and Marcelo Delgado, for being brothers from another mother, and often times reflections of myself from a parallel universe. Also, to every person and experience that I have encountered, good or bad, for making me who I am today. vi ABSTRACT OF THE DISSERTATION AB INITIO QUANTUM CHEMICAL STUDIES ON NEUTRAL-RADICAL REACTIONS OF ETHYNYL (C2H) AND CYANO (CN) WITH UNSATURATED HYDROCARBONS by Adeel Jamal Florida International University, 2012 Miami, Florida Professor Alexander Mebel, Major Professor An Ab Initio/RRKM study of the reaction mechanism and product branching ratios of neutral-radical ethynyl (C2H) and cyano (CN) radical species with unsaturated hydrocarbons is performed. The reactions studied apply to cold conditions such as planetary atmospheres including Titan, the Interstellar Medium (ISM), icy bodies and molecular clouds. The reactions of C2H and CN additions to gaseous unsaturated hydrocarbons are an active area of study. NASA’s Cassini/Huygens mission found a high concentration of C2H and CN from photolysis of ethyne (C2H2) and hydrogen cyanide (HCN), respectively, in the organic haze layers of the atmosphere of Titan. The reactions involved in the atmospheric chemistry of Titan lead to a vast array of larger, more complex intermediates and products and may also serve as a chemical model of Earth’s primordial atmospheric conditions. The C2H and CN additions are rapid and exothermic, and often occur barrierlessly to various carbon sites of unsaturated hydrocarbons. The reaction mechanism is proposed on the basis of the resulting potential energy surface (PES) that includes all the possible intermediates and transition states that can occur, and vii all the products that lie on the surface. The B3LYP/6-311g(d,p) level of theory is employed to determine optimized electronic structures, moments of inertia, vibrational frequencies, and zero-point energy. They are followed by single point higher-level CCSD(T)/cc-vtz calculations, including extrapolations to complete basis sets (CBS) of the reactants and products. A microcanonical RRKM study predicts single-collision (zero-pressure limit) rate constants of all reaction paths on the potential energy surface, which is then used to compute the branching ratios of the products that result. These theoretical calculations are conducted either jointly or in parallel to experimental work to elucidate the chemical composition of Titan’s atmosphere, the ISM, and cold celestial bodies. viii TABLE OF CONTENTS CHAPTER PAGE 1. INTRODUCTION 1 1. Titan’s Chemistry 2 2. Photochemical Models 4 3. Ethynyl and Cyano Radicals 7 2. BACKGROUND 10 1. Astrochemical Observations 10 2. Previous Ab Initio Studies 13 3. COMPUTATIONAL METHODS 16 1. Molecular Orbital Theory 19 1. Variational Principle 20 2. Born-Oppenheimer Approximation 21 3. Self-Consistent Field Method 22 2. Ab Initio Quantum Chemistry 23 1. Hartree-Fock Theory 23 2. Coupled Cluster Theory 25 2. Basis Set 27 1. Gaussian-Type Functions 27 2. Split-Valence Functions 29 3. Polarization Functions 30 4. Diffuse Functions 30 5. Correlation Consistent Functions 31 3. Density Functional Theory 31 1. Kohn Sham Self-Consistent Field 32 2. Hybrid Functionals 33 4. Statistical Theory of Reaction Rates 34 1. Transition State Theory 35 2. Lindemann-Hinshelwood Theory 36 3. RRK Theory 38 4. RRKM Formalism` 39 5. Master-Equation Methods 40 4. C2H RADICAL REACTIONS 42 1. C2H + Allene 43 1. Reaction Mechanism 43 2. Product Brancing Ratios 56 2. C2H + Methylacetylene 61 1. Reaction Mechanism 62 2. Product Brancing Ratios 66 3. C2H + 1,3-Butadiene 68 ix 1. Reaction Mechanism 69 2. Product Brancing Ratios 71 4. C2H + 1,2-Butadiene 72 1. Reaction Mechanism 72 2. Product Brancing Ratios 82 5. C2H + 1-Butyne 84 1. Reaction Mechanism 86 2. Product Brancing Ratios 97 6. C2H + 2-Butyne 100 1. Reaction Mechanism 101 2. Product Brancing Ratios 103 5. CN RADICAL REACTIONS 104 1. CN + Diacetylene 104 1. Reaction Mechanism 105 2. CN + 1,2-Butadiene 107 1. Reaction Mechanism 108 2. Product Brancing Ratios 114 3. CN + 1- Butyne 116 1. Reaction Mechanism 117 2. Product Brancing Ratios 121 4. CN + 2-Butyne 123 1. Reaction Mechanism 124 2. Product Brancing Ratios 126 6. COMPARISONS WITH EXPERIMENT 128 1. Reaction of C2H + C3H4 128 2. Reaction of C2H + 1,3-Butadiene 130 3. Reaction of C2H + 1-Butyne 133 4. Reaction of CN + Diacetylene 140 7. CONCLUSIONS 143 1. H-loss vs CH3-loss Reaction Channels 144 2. Isoelectronic Product Comparisons 148 REFERENCES 150 APPENDICES 157 VITA 276 x LIST OF TABLES TABLE PAGE Table 4.1: Product Branching Ratios of C2H + allene 58 Table 4.2: Product Branching Ratios of C2H + methylacetylene 67 Table 4.5: Product Branching Ratios of C2H + 1-butyne 98 Table 4.6: Product Branching Ratios of C2H + 2-butyne 103 Table 5.2: Product Branching Ratios of CN + 1,2-butadiene 115 Table 5.3: Product Branching Ratios of CN + 1-butyne 122 Table 5.4: Product Branching Ratios of CN + 2-butyne 127 Table 6.3: Adiabadic & Vertical Ionization Potential
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