Speaker
Description
Atoms and molecules excited to a Rydberg state possess one electron residing predominantly far away from the ion core. For sufficiently large values of the principal and/or orbital-angular-momentum quantum numbers of the Rydberg electron, the ion core can be considered as isolated from the Rydberg electron. Its structure and dynamics are, to a good approximation, the same as the bare ion. This property lies, for example, at the heart of the isolated core excitation (ICE) technique widely used to study the core-excited Rydberg states of alkaline-earth-metal atoms.
In this talk, I will discuss how electronically excited states of molecular ions can be studied by probing the isolated ion core of a molecule in a high Rydberg state. High-resolution spectroscopy techniques have been developped for this purpose and include action spectroscopy schemes based on molecular photodissociation or quantum-control multiphoton schemes. These techniques were used to carry out the first characterization the Rydberg states of a molecular cation, with the example of the MgAr$^+$ ion. The Rydberg states of molecular ions are poorly known compared to the Rydberg states of neutral molecules, despite the fact that the former play an important role for high-resolution photoelectron spectroscopy of cations and act as transient resonances in ion-neutral collisions. Our study paves the way to systematic investigations of the Rydberg states of molecular cations.
When the ion core within the Rydberg-electron orbit is excited to a sufficiently high electronic state, it can no longer be considered as isolated from the Rydberg electron and electronic correlations play an important role. As noted by others, the transition from the isolated-core regime to the regime where correlations are important offers interesting insights into electronic correlations. Electronic states of Mg and Sr atoms in which both of their valence electrons are highly excited are ideal to study these correlations. I will present the results of joint experimental and theoretical investigations of the so-called planetary states of Mg and Sr, with particular emphasis on the role played by correlations in the two-electron dynamics.
