Ultracold Molecular Structure and Collisions

Ultracold molecules are instrumental in many fields of physics, such as high-resolution spectroscopy, quantum computation, and cold controlled chemistry. In this dissertation, we discuss the structure and collisions of ultracold molecules in the presence of external magnetic fields. We explore these topics in four main projects. First, we study ultracold chemical reactions of triplet-state NaLi ( a 3 Σ + ) molecules with Na atoms in the presence of an external magnetic field. We observe that by tuning the magnetic field to a Feshbach resonance or by starting the reactants in their fully spin-polarized hyperfine and rovibrational states, the NaLi ( a 3 Σ + )+Na→Na 2 +Li reaction can be suppressed by several orders of magnitude. Second, we propose a mechanism to tune the electric dipole moments and long-range dipolar interactions of polar alkali-dimer molecules (such as KRb) with external magnetic fields. We find that this tunability is possible due to the quantum ergodicity of molecular eigenstates at low magnetic fields and the avoided crossings caused by the nuclear-electric quadrupole interaction. Third, we use a rigorous coupled-channel method to examine quantum nuclear spin dynamics in cold collisions between 13 C 16 O molecules and He atoms. We found that the transition rates depend on the initial and final state's projections of rotational and nuclear spin angular momenta ( M N and M I ). We observed that certain transition rates are dependent on the magnetic field, and explained this dependence using the first Born approximation. We utilize the transition rates we have calculated to find the nuclear spin relaxation rate of 13 C 16 O in a helium buffer gas. We find the relaxation rates are highly dependent on temperature. Finally, we demonstrate that cold collisions between 13 C 16 O molecules and He atoms can be used, in combination with microwave pumping, to produce cold spin-polarized molecules with high efficiency (≥ 95%) at 1 K. This is accomplished by pumping the molecules to the first rotational excited state and allowing spin and rotational state-changing collisions to occur, which populate a single final spin state.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctorate Degree

Grantor

University of Nevada, Reno

Year dc:date.issued

2024

Author dc:creator

• Hermsmeier, Rebekah K. T.

Advisor dc:contributor.advisor

• Tscherbul, Timur

Committee members dc:contributor.committeemember

• White, Thomas
• Weinstein, Jonathan
• Safronova, Alla
• Odoh, Samuel

Repository record dc:identifier.uri

https://scholarwolf.unr.edu/handle/11714/10974

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/10974