• HD⁺is made up of a hydrogen atom (protium) and a deuterium atom, both bound to an electron. It's the simplest type of molecular ion with different kinds of nuclei. Doing really accurate spectral experiments on HD⁺is super important for understanding how three - body systems work when they're bound together. The frequencies at which HD⁺vibrates and rotates are related to the masses of the nucleus and the electron. So, by putting together theory and experiments, we can use the very precise spectrum of HD⁺to figure out related physical constants. For example, we can find the "proton-electron mass ratio," which is a constant that doesn't have any units.

Molecular Hydrogen (HD⁺) Ions

 

• In recent years, preparing (ultra-) cold molecules and molecular ions has become a trendy research topic. The problem is that most molecular ions don't have a simple, repeating cycle for energy transitions. This is the biggest roadblock for directly using lasers to cool them down. However, sympathetic cooling, which relies on the Coulomb interaction between laser-cooled ions and other ions that cannot be directly laser-cooled, is a highly effective approach for cooling molecular ions. This method has substantially advanced the research on (ultra-) cold molecular ions.

A bi-component Coulomb Crsytal of Be⁺/HD⁺ ions

• A beryllium ion (Be⁺) has a beryllium nucleus and three electrons. It’s the simplest atomic ion directly laser-coolable. Accurate spectral experiments on Be⁺are key to understanding bound four-body systems. Measuring its spectrum tests QED predictions on fine/hyperfine structure and the Lamb shift precisely. This refines quantum field theory and other basic physics theories.

• Studying how Be⁺ions react with H₂/HD molecules helps us understand basic chemical processes and reaction dynamics at the atomic and molecular levels. These reactions display isotope effects because hydrogen and deuterium have different masses. This work shows bond formation/breakage during ion-molecule interactions and uncovers factors influencing product selectivity, like isotopologue formation or energy distribution.

Be⁺/BeH⁺/BeD⁺ multi-component crystals after reactions