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Equilibrium and Dynamic Studies of the Van Der Waals Molecule Titanium-Helium: Tihe

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Equilibrium and Dynamic Studies of the Van Der Waals Molecule Titanium-Helium: Tihe University of Nevada, Reno Equilibrium and dynamic studies of the van der Waals molecule titanium-helium: TiHe A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics by Nancy P. Quir´osAguilar Dr. Jonathan D. Weinstein/Dissertation Advisor August 2016 THE GRADUATE SCHOOL We recommend that the dissertation prepared under our supervision by NANCY P. QUIRÓS AGUILAR Entitled Equilibrium and dynamic studies of the van der Waals molecule titanium-helium: TiHe be accepted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Jonathan D. Weinstein, Ph.D., Advisor Timur Tscherbul, Ph.D., Committee Member Robert Guyer, Ph.D., Committee Member Roberto Mancini, Ph.D., Committee Member David Leitner, Ph.D., Graduate School Representative David W. Zeh, Ph. D., Dean, Graduate School August, 2016 i Abstract Atoms that are weakly bound by the van der Waals (vdW) interaction are called van der Waals molecules. Conditions for the existence and formation of vdW molecules are favorable at low temperatures due to their weak binding energy. In the exper- iment described in this thesis, we used laser ablation and He buffer gas cooling to form the exotic vdW molecule titanium-helium: TiHe. A spectroscopic search for the TiHe molecule was initially conducted near the 3 3 −1 a F2 ! y F2 atomic Ti transition at 25107:410 cm . Several laser-induced-fluorescence signals were found and studied. However, it was not possible to conclude that these peaks corresponded to a bound TiHe molecule. We continued the search for TiHe and multiple transitions were found closely blue 3 3 −1 detuned from the a F2 ! y F3 atomic Ti transition at 25227.220 cm . Measure- ments of the TiHe binding energy were obtained from the study of its equilibrium thermodynamic properties and good agreement with theoretical predictions for the molecule's binding energy was obtained. The creation of the TiHe molecule is of great significance, since TiHe has interesting properties: TiHe possesses an anisotropic in- teraction due to its non zero angular momentum and it is the first neutral molecule characterized by the Hund's case e). We believe that TiHe was formed from the constituent cold atoms through three body recombination. Progress towards measuring the three body recombination rate coefficient K3 will be discussed and preliminary values of this coefficient will be shown. ii Dedicada a mi mam´aLucy y a mi pap´aBernardo. iii Acknowledgements I would like to express my deepest gratitude to my advisor Prof. Jonathan D. We- instein for his patience, support and for sharing his knowledge. Without his guidance, this dissertation would not have been possible. I also want to thank the members of my committee: Prof. Timur Tscherbul, Prof. Robert Guyer, Prof. Roberto Mancini and Prof. David Leitner for their invaluable advice. Special thanks to Prof. Timur Tscherbul for his theoretical work on TiHe. I want to thank Prof. David Leitner for being an excellent instructor and motivating me to pursue teaching in the future. I want to acknowledge the lab members that collaborated in this experiment: Naima Tariq for her work on the spectroscopic search of TiHe. My friend Jocelyn Sanchez and Andrew Kanagin for their contribution in the measurement of the three body recombination coefficient. Also, thanks to Sunil Upadhyay for his input on the experiment during the Monday meetings. Finally, I want to give special thanks for the love, support, and friendship to God, my big loving family: my parents (Lucy and Bernardo), my brothers (Jonathan and Cristopher), my grand parents (Bernardo, Claudia and Lourdes), my aunts and uncles (especially Vane, Carlos A-B, Joyce and Freddy), my fianc´eMartin and my friends: old and new ones. iv Contents Abstract.....................................i Dedication.................................... ii Acknowledgements............................... iii Contents..................................... iv List of Tables.................................. vii List of Figures.................................. ix 1 Introduction1 1.1 Types of molecular bond.........................1 1.1.1 Intramolecular bonds.......................2 1.1.2 Intermolecular bonds.......................2 1.2 Cold molecules..............................4 1.2.1 Cold molecules applications...................5 1.2.2 Making cold molecules......................7 1.3 Past work on cold vdW molecules....................8 1.3.1 Molecules with He attached...................9 1.4 TiHe formation.............................. 11 1.4.1 Three body recombination process............... 11 1.5 Summary of upcoming chapters..................... 13 2 TiHe Binding Energy Estimate 15 2.1 Basics on Molecular Spectroscopy.................... 15 2.2 TiHe ground state potential....................... 17 2.3 TiHe ground state vibrational levels................... 19 2.4 TiHe rotational levels of the ground state................ 21 2.5 Excited state of the TiHe molecule................... 22 v 3 TiHe Experiment 33 3.1 Cryogenic System............................. 33 3.2 Detection of Titanium (Ti)........................ 35 3.3 Detection of TiHe............................. 42 3.3.1 Fluorescence detection improvement.............. 44 3.4 Measurement of He density........................ 46 3.5 Measurement of Ti density........................ 47 3.6 Measurement of temperature....................... 48 3 3 4 TiHe signals at a F2 ! y F2 Ti transition 65 3 3 4.1 Spectroscopic search of TiHe at a F2 ! y F2 Ti transition...... 65 4.2 Equilibrium thermodynamic studies................... 67 4.2.1 Blue detuned spectroscopic TiHe signal............. 68 4.2.1.1 Ti dependence..................... 69 4.2.1.2 Temperature dependence................ 69 4.2.1.3 He dependence..................... 73 4.2.2 Red detuned spectroscopic TiHe signal............. 75 4.2.2.1 Ti dependence..................... 75 4.2.2.2 Temperature dependence................ 76 4.2.2.3 He dependence..................... 77 3 3 5 TiHe signals at a F2 ! y F3 Ti transition 91 3 3 5.1 Spectroscopic search of TiHe at a F2 ! y F3 Ti transition...... 92 5.2 Equilibrium thermodynamic studies................... 96 5.2.1 TiHe signal at 25228.15 cm−1 .................. 96 5.2.1.1 Ti dependence..................... 96 5.2.1.2 Temperature dependence................ 96 5.2.1.3 He dependence..................... 98 5.2.2 TiHe signal at 25228.03 cm−1 .................. 98 5.2.2.1 Ti dependence..................... 98 5.2.2.2 Temperature dependence................ 98 5.2.2.3 He dependence..................... 99 5.2.3 TiHe signal at 25228.10 cm−1 .................. 100 5.2.3.1 Ti dependence..................... 100 5.2.3.2 Temperature dependence................ 100 5.2.3.3 He dependence..................... 101 vi 5.2.4 TiHe signal at 25227.99 cm−1 .................. 101 5.2.4.1 Ti dependence..................... 101 5.2.4.2 Temperature dependence................ 101 5.2.4.3 He dependence..................... 101 5.2.5 Variations in nHe measurements................. 102 5.2.6 Identification of the TiHe peaks................. 104 5.2.6.1 Thermodynamic dependence.............. 104 5.2.6.2 Isotope shifts...................... 105 5.2.6.3 Comparison between experimental results and theo- retical predictions................... 107 6 Measurement of the three body recombination coefficient K3 135 6.1 Photodissociation experiments...................... 137 6.1.1 TiHe cross section (σTiHe).................... 141 6.2 Experimental set up........................... 143 6.3 Upper limit of K2 ............................. 144 6.4 Beam waist (wx; wy)=(0.8, 0.5) mm................... 145 6.4.1 Saturation curves......................... 145 6.4.1.1 Peak at 25228.15 cm−1 ................ 145 6.4.1.2 Peak at 25228.03 cm−1 ................ 146 6.4.2 K2 and K3 ............................. 147 6.5 Beam waist (wx; wy)=(0.4, 0.3) mm................... 148 6.5.1 Saturation curves......................... 148 6.5.1.1 Peak at 25228.15 cm−1 ................ 148 6.5.1.2 Peak at 25228.03 cm−1 ................ 148 Bibliography 169 vii List of Tables 2.1 Calculated TiHe ground state binding energies for the rotational lev- els l = 0,1,2 in units of J, cm−1, K and eV using the Lennard-Jones potential.................................. 21 2.2 Calculated TiHe ground state binding energies for the rotational levels l = 0,1,2 in units of J, cm−1, K and eV using the Buckingham potential. 21 4.1 Binding energies and their relative uncertainty obtained at studying the temperature dependence of the TiHe interaction found at 25108.27 cm−1 at different He densities...................... 75 4.2 Binding energies and their relative uncertainty obtained at studying the temperature dependence of the TiHe interaction found at 25103.67 cm−1 at different He densities...................... 76 5.1 Binding energies and their relative uncertainty obtained at studying the temperature dependence of the TiHe interaction found at 25228.15 cm−1 at different He densities...................... 97 5.2 Binding energies and their relative uncertainty obtained at studying the temperature dependence of the TiHe interaction found at 25228.03 cm−1 at different He densities...................... 99 5.3 Binding energies and their relative uncertainty obtained at studying the temperature dependence of the TiHe interaction found at 25228.10 cm−1 at different He densities...................... 100 5.4 Binding energies and their relative uncertainty obtained at studying the temperature dependence
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