06 Atomic and Molecular Physics

The existence of atoms was not fully accepted until just over 100 years ago although the concept had been around for millennia. Now, with a fully-developed quantum theory of atomic and molecular structure, we possess remarkable tools for manipulating atoms and exploring their structure, dynamics, and interaction to exquisite precision. Consider the simplest of all atoms: hydrogen, composed of a single proton and a single electron that each are characterized by mass, charge, and spin. What determines the size of the structure formed by these constituents and how can we measure this size? How can the particle interactions be fully described and probed through further interactions with electromagnetic fields (including light) or with other atoms? What happens when the proton is replaced with a bound proton and neutron as the nucleus to form the isotope called deuterium? What does detailed knowledge of this basic hydrogen system reveal of the behavior of other more complex atoms? Why indeed can we infer so much about more complex atoms from the quantum states elucidated for the hydrogen atom. What new features occur when atoms become more complex? What further elaborations of energy states and interactions will occur when atoms bind as molecules and how can we probe the relationship between molecular bonds and the electron states within the system of atoms making up the molecules? It is now possible to manipulate atoms singly or in populations trapped by various means. What new physics does this capability allow? Also, what happens when we form atom or ion beams that then interact with external fields, electromagnetic radiation, and other atoms? There is an enormous microcosm of the universe to be explored at this fundamental scale of nature.Image source: PoorLeno, Public domain, via Wikimedia Commons