Cold Chemistry and Precision Spectroscopy of CaH+ Molecular Ions

Abstract

The complex internal structure of molecules, encompassing electronic, vibrational, and rotational states, offers unique opportunities to study fundamental physics and chemistry, enable quantum information processing, and probe the formation of structures in the universe. However, this same structural complexity makes molecules and molecular ions challenging to control and manipulate directly, as the standard techniques developed for atomic systems are often inapplicable. In this dissertation, we leverage the precision control methods established for atomic species to study and probe molecular ions by co-trapping them with atomic species.The ability to co-trap atomic calcium ions (40Ca+), neutral potassium atoms (39K), and calcium hydride molecular ions (CaH+) in our experimental setup enables the investigation of fundamental properties of molecular ions. Two key studies are presented. First, we report evidence of charge exchange interactions between CaH+ and 39K in the regime of cold chemistry. We measure the rate coefficient for this interaction, finding it to be an order of magnitude smaller than the Langevin rate and independent of the internal state of the 39K atoms. These experimental observations are complemented by quantum chemical calculations modeling the CaH+-K system in both ground and excited electronic states, offering insights into the observed reaction rate and testing the validity of quantum chemistry methods.Second, we use resonance-enhanced multi-photon dissociation (REMPD) spectroscopy to perform high-resolution rovibronic spectroscopy of CaH+. Focusing on the rotational transitions within the |X1Σ+,ν” = 0⟩→|A1Σ+,ν′ = 2⟩manifold, we resolve individual P- and R-branch transitions with record precision. Using Fortrat analysis, we extract key spectroscopic constants for the |A1Σ+,ν′ = 2⟩state, including the band origin, rotational constant, and centrifugal distortion correction. Furthermore, we demonstrate in-situ black-body thermometry by utilizing the observed spectra to extract the local thermal environment temperature.These studies underscore the utility of hybrid ion-atom traps for investigating fundamental properties of molecular ions. Both the charge exchange experiments and the precision spectroscopy measurements presented in this dissertation serve to advance our understanding of fundamental chemical processes. Additionally, this work contributes to the development of techniques for controlling and manipulating molecular ions, providing a foundation for future efforts to achieve full quantum control over these systems and unlock their potential for diverse scientific and technological applications.