Excited states of atoms and molecules exhibit a rich array of diverse phenomena. This dissertation examines two exotic states of atoms at such excited levels: Rydberg molecules and atomic negative ions. Rydberg molecules are formed by a Rydberg atom and one or more ground state atoms, and can be highly polar due to their unusual electronic wave functions and enormous bond lengths. This dissertation expands the theory of these molecules by studying the formation and structure of polyatomic molecules, multichannel Rydberg molecules formed from divalent atoms, and spin effects and relativistic interactions. It also details intermolecular forces between Rydberg molecules, their manipulation via external fields, and their dependence on the intricacies of electron-atom scattering. This electron-atom interaction is also the main component of the latter portion of this thesis, which studies doubly excited states of alkali negative ions in very polarizable and nearly degenerate atomic states. Photodetachment of these states reveals electron correlation and long-range forces stemming from their high excitation.
Excited states of atoms and molecules exhibit a rich array of diverse phenomena. This dissertation examines two exotic states of atoms at such excited levels: Rydberg molecules and atomic negative ions. Rydberg molecules are formed by a Rydberg atom and one or more ground state atoms, and can be highly polar due to their unusual electronic wave functions and enormous bond lengths. This dissertation expands the theory of these molecules by studying the formation and structure of polyatomic molecules, multichannel Rydberg molecules formed from divalent atoms, and spin effects and relativistic interactions. It also details intermolecular forces between Rydberg molecules, their manipulation via external fields, and their dependence on the intricacies of electron-atom scattering. This electron-atom interaction is also the main component of the latter portion of this thesis, which studies doubly excited states of alkali negative ions in very polarizable and nearly degenerate atomic states. Photodetachment of these states reveals electron correlation and long-range forces stemming from their high excitation.
Abstract This PhD tutorial discusses ultra-long-range Rydberg molecules, the exotic bound states of a Rydberg atom and one or more ground state atoms immersed in the Rydberg electron’s wave function. This novel chemical bond is distinct from an ionic or covalent bond, and is accomplished by a very different mechanism: the Rydberg electron, elastically scattering off of the ground state atoms, exerts a weak attractive force sufficient to form the molecule in long-range oscillatory potential wells. In the last decade this topic has burgeoned into a vibrant and mature subfield of atomic and molecular physics following the rapidly developing capability of experiment to observe and manipulate these molecules. This tutorial focuses on three areas where this experimental progress has demanded more sophisticated theoretical descriptions: the structure of polyatomic molecules, the influence of electronic and nuclear spin, and the behavior of these molecules in external fields. The main results are a collection of potential energy curves and electronic wave functions which together describe the physics of Rydberg molecules. Additionally, to facilitate future progress in this field, this tutorial provides a general overview of the current state of experiment and theory.
Rydberg molecule, formed by one or more Rydberg atoms, exhibits remarkable properties, including an exceptionally large spatial extent, rich rovibrational level structures, permanent electric dipole moments, and a pronounced sensitivity to external fields. Based on the underlying binding mechanisms, Rydberg molecules can be divided into three categories, the ground-Rydberg molecule that is bound via a low-energy electron-atom scattering interaction between ground atom and Rydberg electron, the Rydberg-Rydberg molecule that is bound via a long-range electrostatic interaction between Rydberg atoms, and the ion-Rydberg molecule that is bound via single- or multi-polar interactions between Rydberg atom and ion. This review focuses on recent theoretical and experimental advances in diatomic Rydberg molecules, covering their formation and binding mechanisms, potential energy curves, experimental observations, and spectroscopic properties, with the aim of providing a comprehensive overview of the current state and future prospects of this rapidly developing field.
Collisions involving Rydberg atoms reveal detailed information on the state of a background medium and can be used as diagnostic probes of temperature and density distributions in a neutral or ionized gas. Spectroscopy of Rydberg atoms in highly excited states reveals the interaction of the Rydberg electron with core electrons, including relativistic effects, and can be used for precise determination of fundamental constants. The advent of ultracold trapping and cooling methods in the last three decades has ushered in a new paradigm in Rydberg physics control and manipulation. The concept of the Rydberg blockade, for instance, al- lows for precise control of long-range dipolar interaction between atoms, creation of correlated many-body wave functions, and realization of macroscopic quantum entanglement and quan- tum logic operations. The formation of a new class of Rydberg molecules arising from ground and Rydberg atom collisions can be used to manipulate electron-atom scattering phase shifts, form and manipulate molecules with enormous permanent electric dipole moments, study Ry- dberg chemistry at the ultracold, and realize macroscopic quantum polaronic systems. In this thesis, I will investigate charge transfer from covalent ground-Rydberg collisions to form heavy ion pair states. In another related study, I explore the formation of spin-mixed ultralong range Rydberg molecules, by accounting for spin-dependent relativistic fine and hyperfine interac- tion. Such studies help to not only explain experimental observations, but also point to how molecular reactions can be controlled using small electric or magnetic fields.
In this thesis, we investigate few-body physics and many-body physics of ultralong-range Rydberg molecules. Ultralong-range Rydberg molecules are formed through scattering processes between Rydberg electrons and ground state atoms. The huge size of the Rydberg electron's orbit makes the Rydberg electron able to interact with more than one ground state atom in cold atomic gases with atom number densities from 1012 cm−3 to 1014 cm−3. In cold atomic gases, the ground state atoms on average are far away from each other. They are weakly interacting. Depending on the angular momentum state of the Rydberg electron, two types of polyatomic Rydberg molecules have been studied. When the Rydberg electron is in an ns state, the isotropic probability distribution of the Rydberg electron makes the Rydberg electron interact with different ground state atoms equally. The total binding energy is a summation of the binding energy from each scattering process. These additive interactions have been studied using Cs 6s+83s and 6s+90s polyatomic Rydberg molecules in this thesis. When the Rydberg electron is in an l>0 angular momentum state, spatial correlations between different ground state atoms are established through the anisotropic probability distribution of the Rydberg electron. The total binding energy depends on the relative positions of different ground state atoms. These nonadditive interactions are studied using Cs 6s+6s+34d and 6s+6s+36d triatomic Rydberg molecules in this thesis.
Ultralong-range Rydberg molecules, composed of an excited Rydberg atom and a ground-state atom, are characterized by large bond lengths, dipole moments, sensitivity to external fields, and an unusual binding mechanism based on low-energy elastic electron scattering. Although Rydberg molecules formed between alkali atoms have received the most attention, the additional complexity found in atoms with more than a single valence electron poses new theoretical challenges as well as new possibilities for control and design of the molecular structure. In this paper, we extend the theory of Rydberg molecules to include the additional spin coupling of the Rydberg states of a multivalent atom. We employ this theory to describe the properties of Rydberg molecules composed of mercury atoms. We calculate the potential energy curves of both heteronuclear (Hg∗Rb) and homonuclear (Hg∗Hg) molecules. In the former case, we propose the realization of long-range spin entanglement and remote spin flip. In the latter, we show how long-lived metastable molecular states of Hg∗Hg exist as resonances above the dissociation threshold.
This talk will present several exciting nuggets from the last half-century of progress in our understanding of Rydberg electron physics in atoms and small molecules. Some key elements of this deepened understanding have emerged from experiments that were understood through the multichannel quantum defect theory developed by Seaton, Fano, Jungen and their collaborators. That powerful combination has enabled spectra of remarkable complexity and richness to be quantitatively understood and qualitatively interpreted using this framework. Another aspect of Rydberg physics connects with Enrico Fermi’s treatment of the interaction between a slow electron and a distant ground state atom, which has been predicted to generate a new chemical bonding mechanism that can bind an exotic long range diatomic or triatomic molecule whose internuclear distances can be as large as a small virus. The production of this class of exotic, weakly-bound Rydberg molecules has been demonstrated in a remarkable series of experiments in the last few years.