PHOTOCHEMICALLY INDUCED REACTIONS BETWEEN OZONE AND HALOGENATED SPECIES: A MATRIX ISOLATION STUDY by Loraine Johanna Foley A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Christopher Ingold Laboratories University College London University of London December 2000 ProQuest Number: U644104 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest U644104 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT The main objective of this research was to study the photochemically induced reactions of ozone with some halogenated species in low temperature matrices, using Fourier-transform infrared spectroscopy, to observe and characterise novel intermediates and to determine pathways for such reactions. Ozone plays a significant role in the chemistry of both the stratosphere and troposphere and thus information concerning the photochemistry of halogenated species in the presence of ozone is of considerable atmospheric importance and is therefore relevant to gas phase atmospheric research. The FT-IR matrix isolation technique is well suited to providing background information on gas phase atmospheric reactions since most atmospheric species exhibit infrared spectra, and the ability to isolate low concentrations of reactive chemical species in the matrix mimics the conditions of dilution in the atmosphere. Thus the results obtained from matrix isolation experiments can complement those obtained from gas phase studies. Since matrix-isolated species are held at very low temperatures, any thermal reactivity is quenched and reactions have to be initiated either photochemically or thermally. In these experiments the matrices are photolysed in order to initiate a reaction by using a range of wavelengths in the visible and UV regions. Any reactive or unstable species produced by irradiation at a particular wavelength are stabilised indefinitely for spectroscopic analysis, thus allowing the photochemical pathway to be revealed. In the matrix the species are held in close proximity to one another allowing secondary reactions to occur that would not have occurred in the gas phase; this has enabled a range of nearest-neighbour complexes to be generated in situ and detected in this study. Of the halogenated species studied, the halogen cyanides, ICN and BrCN, were separately co-deposited with ozone and the photo-induced reactions are reported. Ozone is shown to form a complex with ICN but not with BrCN and so the photochemistry of ozone is altered in the O 3/ICN reaction, allowing the formation of several new species to be observed. Harsh UV irradiation is required to initiate a reaction in the Og/BrCN matrix, as well as in the reactions between ozone and the trihalomethanes (CHBr 2Cl and CHBrCb) where several novel carbonyl*“ Lewis acid and carbon monoxide * * *Lewis acid complexes were detected. The co-deposition of ozone with each of the halogenated ethenes, BrCH=CHBr and C1CH=CHC1, led to the formation of a charge transfer complex which dissociates to form several new species including carbonyl and carbon monoxide species. Finally, the photo-induced reaction of ozone with some diiodo-species highlights the different photochemical behaviour of a molecule containing two iodine atoms as distinct from one in the presence of ozone. In each case the photoproducts were identified by FT-IR spectroscopy and photochemical pathways proposed. In some instances nitrogen dioxide and solid oxygen matrices were used to provide alternative sources of O atoms for reaction. Ill ACKNOWLEDGEMENTS There are many people who I would like to thank for contributing in one way or another towards the completion of this thesis. First I must thank Professor Robin Clark who over these last years has given me a considerable amount of support, encouragement, and knowledgeable advice, but most of all, his time. I also thank Dr Stephen Price for arranging the valuable and informative group meetings in the early stages and who was always there to give good advice when things were not going to plan. Thanks go to Dr Ian Bell, who at the beginning gave me guidance, and later on, to Dr Steven Firth for listening and for always knowing the answers to my questions. I am also grateful to Dr Steven Firth for his constant help, while I was overseas, in the final production of this thesis. A special thanks goes to Jon Darm for teaching me the matrix isolation technique and who’s own research gave inspiration towards some of the work in this thesis. Any mention of thanks with regard to Lab 132 would not be complete without thanking the rest of the Clark research group (Katherine, Amanda, Lucia, Joe, Marcia, and Paulina) for maintaining an interesting and fun environment to work in. I must also take this opportunity in thanking Dr Andrea Sella for his help with the preparation of some of the samples used in these experiments and also for his advice concerning seminar presentations. An appreciative thanks goes to Dr Sean McGrady due to a problem concerning the cryogenic apparatus being resolved after a chance meeting. Regarding the maintenance of the equipment used in this thesis, I must convey my deepest appreciation to the members of the workshop, especially to John Hill, Dave Knapp, and Dick Way mark, without whom, there would have been no research and thus no thesis; I am truly indebted to each of them. Last, but especially not least, so many ‘thank yous’ have to go to my family and friends. In particular, to my Mum and Dad for having always believed in me and giving me so much support, without them the past years would have been a lot harder and 1 truly thank them for everything. I thank the rest of my family, especially my nieces and nephews, for keeping things real and also all my friends for just being there and sharing the fun times with me. Finally an enormous amount of respect and affection goes to Marvin who is such a positive influence in all areas of my life, who understands and believes in me and who is such an abundant source of spiritual strength, but most of all, who makes me laugh, - thanks! IV TABLE OF CONTENTS Abstract ii Contents V List of Figures viii List of Tables X List of Schemes xii List of Abbreviations xiii CHAPTER 1 INTRODUCTION 1 1.1 M atr ix Iso latio n 2 1.2 A ims of Research 3 1.2.1 Choice of P recursors 4 1.3 Thesis O utline 6 1.4 References 8 CHAPTER 2 EXPERIMENTAL AND THEORY 11 2.1 Introduction 12 2.2 Properties of M atrix M aterials 12 2.3 In fr a r ed S pectroscopy 15 2.3.1 M o lecular S pectroscopy 15 2.3.2 Instrumentation 20 2.4 Experim ent a n d P rocedure 25 2.4.1 A ppa r a tu s 25 2.4.2 Experimental Procedure 29 2.5 References 33 CHAPTER 3 PHOTOCHEMICALLY INDUCED REACTIONS OF IODINE CYANIDE 35 3.1 Introduction 36 3.2 Io d in e Cy a n id e a n d O zone 37 3.2.1 Resu lts AND D iscussio n 37 3.2.2 Photochemical Path w a y 47 V 3.3 Iodine Cy a n id e a n d N itrogen D io xide 55 3.3.1 Resu lts a n d D isc u ssio n 55 3.3.2 Photochemical P a th w a y 58 3.4 Con c lu d in g Rem a rk s 62 3.5 References 62 CHAPTER 4 PHOTOCHEMICALLY INDUCED REACTIONS OF BROMINE CYANIDE 65 4.1 Introduction 66 4.2 Bromine Cyanide and Ozone 66 4.2.1 Resu lts a n d D isc u ssio n 67 4.2.2 Photochemical P a th w a y 72 4.3 B rom ine Cy a n id e a n d N itro gen D ioxide 77 4.3.1 Resu lts a n d D iscu ssio n 77 4.3.2 P hotochemical P a th w a y 79 4.4 Co n cluding Rem ark s 83 4.5 References 84 CHAPTER 5 PHOTOCHEMICALLY INDUCED REACTIONS OF DIBROMOCHLOROMETHANE AND BROMODICHLOROMETHANE 86 5.1 Introduction 87 5.2 DIBROMOCHLOROMETHANE AND OZONE 88 5.2.1 Results and Discussion 88 5.2.2 Photochemical Pa th w a y 95 5.3 BROMODICHLOROMETHANE KH 5.3.1 Re su lts AND D iscu ssio n 101 5.3.2 P hotochemical Pa th w a y 109 5.4 Co ncluding Rem ark s 115 5.5 References 115 CHAPTER 6 PHOTOCHEMICALLY INDUCED REACTIONS OF 1,2-DIBROMOETHENE AND 1,2-DICHLOROETHENE 117 VI 6.1 Introduction 118 6.2 1 ,2 -D ibromoethene 119 6.2.1 Resu lts a n d D iscussio n 120 6.2.2 P hotochemical Path w ay 131 6.3 1 ,2 -D ichloroethene 143 6.3.1 Resu lts a n d D iscussio n 143 6.3.2 P hotochemical Pa th w a y 152 6.4 Co n c lu d in g Rem ark s 166 6.5 References 166 CHAPTER 7 PHOTOCHEMICALLY INDUCED REACTIONS OF DHODOMETHANE AND 1,2-DIIODOETHANE 170 7.1 Introduction 171 7.2 D iiodomethane a n d O zone 171 7.2.1 Re s u l t s AND D is c u s s io n 172 7.2.2 P hotochemical Pa th w ay 176 7.3 1,2-D iiodoethane AND Ozone 182 7.3.1 Re s u l t s AND D is c u s s io n 182 7.3.2 P hotochemical Pa th w a y 186 7.4 C o n c l u d i n g Re m a r k s 191 7.5 References 191 CHAPTER 8 CONCLUSIONS AND FURTHER WORK 193 8.1 Co n c lu sio n s 194 8.2 S u g g estio n s FOR Further W ork 195 8.3 References 198 APPENDIX 199 A1 O zo n e, O3 200 A2 Nitrogen Dioxide, NO2 202 Vll LIST OF FIGURES 1.1.1 A theoretical view of a noble gas matrix 2 2.3.1 The symmetry and fundamental vibrations of a CO 2 molecule 19 2.3.2 Schematic diagram of a Michelson FT-IR spectrometer 22 2.3.3 Schematic diagram of a Genzel interferometer 22 2.4.1 Schematic diagram