Initial Investigations of the Magnetic Circular Dichroism of Isobutene using Synchrotron Radiation in the Vacuum Ultraviolet Region By Clifford Sanders A Thesis Submitted to the Faculty of The Charles E. Schmidt College of Science in Partial Fulfillment of the Requirements for the Degree of Master of Science Florida Atlantic University Boca Raton, Florida August 2009 ii Acknowledgements The author wishes to thank the staff of Florida Atlantic University, Committee members Dr. Snyder, Dr. Perumareddi and Dr. Medina (a grand thanks to Dr. Medina). The author thanks Vonnie Sanders (mother) for always being supportive. The author gives a special thanks to his wife, Keji, for her understanding. The author also wishes to thank Evelyn Hall, Jennie Soberon, and Cora Woodman for their continued efforts in assisting with his enrollment. Most of all, the author wishes to thank Dr. Narayanan for keeping the author‟s best interest in mind. iii Abstract Author: Clifford Sanders Title: Initial Investigations of the Magnetic Circular Dichroism of Isobutene using Synchrotron Radiation in the Vacuum Ultraviolet Region Institution: Florida Atlantic University Thesis Advisor: Professor Patricia Ann Snyder Degree: Master of Science Year: 2009 Ethylene is the simplest alkene. The carbon–carbon double bond is ubiquitous in the field of chemistry. Ethylene serves as the basis for understanding these molecules. Thus, the assignment of the electronic transitions in ethylene is an important endeavor that many scientists have undertaken, but are yet to decipher theoretically or experimentally. Synchrotron Radiation in the vacuum ultraviolet region allows for magnetic circular dichroism (MCD) measurements of ethylene and other simple alkenes. Studies of ethylene and propylene revealed that the * (AgB1u ethylene notation) transition is not the lowest energy transition. The 3s(R) (AgB3u ethylene notation) is the lowest energy transition. iv To further this investigation, MCD and absorption measurement were carried out on isobutene. The isobutene spectra clearly showed four electronic transitions in the 156 to 212 nm wavelength region. These four isobutene transitions have been assigned as 3s, *, 3pσ and 3px proceeding from lower energy to higher energy. The present results support the assignments in ethylene and propylene. v Initial Investigations of the Magnetic Circular Dichroism of Isobutene using Synchrotron Radiation in the Vacuum Ultraviolet Region List of Figures .................................................................................................................. viii List of Tables ...................................................................................................................... x List of Equations ................................................................................................................ xi 1. Introduction .................................................................................................................... 1 2. Electromagnetic radiation .............................................................................................. 5 Polarization ................................................................................................................. 9 Linear polarization ..................................................................................................... .9 Circularly polarization .............................................................................................. 10 Absorption of radiation ............................................................................................. 12 Circular dichroism/Magnetic circular dichroism ...................................................... 15 Synchrotron radiation................................................................................................ 16 3. Theory .......................................................................................................................... 19 Molecular orbitals ..................................................................................................... 19 The importance of symmetry .................................................................................... 23 Group theory ............................................................................................................. 23 Matrix Representations ............................................................................................. 26 Character table .......................................................................................................... 27 4. Electronic transitions ................................................................................................... 31 vi Spin selection rules ................................................................................................... 32 Orbital selection rules ............................................................................................... 33 Valence transitions .................................................................................................... 34 Rydberg transitions…………………………………………………………………34 Allowed transitions ................................................................................................... 35 5. Experimental details..................................................................................................... 39 Instrumentation ......................................................................................................... 39 Data reduction ........................................................................................................... 42 6. Experimental Results and Discussion .......................................................................... 45 Isobutene spectra ....................................................................................................... 45 Ethylene and propylene spectra ................................................................................ 46 Isobutene assignments .............................................................................................. 48 Vibrational coupling ................................................................................................. 54 7. Conclusion ................................................................................................................... 61 Appendix ........................................................................................................................... 64 References ......................................................................................................................... 71 vii List of Figures Figure 1.1: Ethylene .......................................................................................................... 1 Figure 1.2: Isobutene ......................................................................................................... 3 Figure 2.1: Electromagnetic wave ..................................................................................... 5 Figure 2.2: Types of interference ....................................................................................... 6 Figure 2.3: Common terms and equations ......................................................................... 7 Figure 2.4: Electromagnetic spectrum .............................................................................. .8 Figure 2.5: Electric field of unpolarized light .................................................................... 9 Figure 2.6: Oscillating electric field for linearly polarized light ..................................... 10 Figure 2.7: Circularly polarized radiation ........................................................................ 11 Figure 2.8: Quarter-wave plate ......................................................................................... 11 Figure 2.9: Synchrotron radiation ..................................................................................... 17 Figure 2.10: Energy range of synchrotron radiation ......................................................... 18 Figure 3.1: „s‟, „p‟, and sp2 hybrid orbitals ....................................................................... 20 Figure 3.2: Bonding and antibonding molecular orbitals of ethylene .............................. 21 Figure 3.3: Molecular orbital structure scheme for molecules containing double bonds . 22 Figure 3.4: Reflection across a plane of symmetry ........................................................... 24 Figure 3.5: Rotation about an axis .................................................................................... 25 Figure 3.6: Inversion about an axis ................................................................................... 25 Figure 3.7: Improper rotation about an axis ...................................................................... 26 viii Figure 3.8: Proper orientation of isobutene ...................................................................... 29 Figure 4.1: Electronic transitions ...................................................................................... 33 Figure 5.1: Basic experimental setup ................................................................................ 40 Figure 5.2: Graph of raw MCD data for isobutene ........................................................... 42 Figure 5.3: Plot of raw MCD data of isobutene and baseline signal ................................ 42 Figure 5.4: Corrected MCD graph of isobutene ..............................................................