Ultralong-range polyatomic Rydberg molecules

Abstract

In this thesis we have theoretically investigated the electronic structure and properties of two types of polyatomic Rydberg molecules, which differ on their binding mechanism. We have first analyzed the impact of an external electric field on a triatomic Rydberg molecule formed by a Rydberg rubidium atom and two ground state rubidium atoms in three geometrical configurations: two collinear arrangements and a planar one. The binding mechanism is based on the low-energy collisions between the Rydberg electron and the ground state atoms. The electronic structure of these triatomic Rydberg molecules is described within the Born-Oppenheimer approximation, and we have used the s- and p-wave Fermi pseudo-potentials to describe the interaction between the Rydberg electron and each of the ground state perturbers. The adiabatic potential curves and surfaces present an oscillatory behaviour as the distance between the ground state atoms and the Rydberg ionic core increases, which is due to the highly oscillatory character of the Rydberg electron wave function. The potential wells of these electronic states are deep enough to accommodate several vibrational levels where the triatomic Rydberg molecule can exist. We have shown that the external electric field enhances the bound character of these adiabatic electronic states. In the second part of this dissertation, we have investigated polyatomic Rydberg molecules formed by a rubidium Rydberg atom and one or two diatomic heteronuclear molecules, being KRb our prototype system. The binding mechanism is due to the anisotropic scattering of the Rydberg electron from the permanent electric dipole moment of the polar molecule. Within the Born-Oppenheimer approximation, we have performed a realistic treatment of the internal rotational motion of the diatomic molecules. For the triatomic Rydberg molecule, we have explored the adiabatic electronic states evolving from the Rydberg manifolds Rb(n; l >= 3), with increasing principal quantum number n, and from the Rydberg states Rb(26d), Rb(28s) and Rb(27p). In all these cases, we have found oscillatory Born-Oppenheimer potentials, with stable configurations, which can accommodate several vibrational bound levels. For the pentaatomic Rydberg molecule, we have considered symmetric and asymmetric linear configurations and have studied the metamorphosis of the Born-Oppenheimer potential curves as the distances between the Rydberg core and the polar molecules increase. Our focus is on the pentaatomic Rydberg molecule formed from the degenerate manifold Rb(n = 20, l >= 3) and the Rydberg state Rb(23s) with ground and rotationally excited KRb diatomic polar molecules, respectively. As in the triatomic Rydberg molecule, we have encountered stable electronic states with potential wells possessing rich vibrational spectra. Since the polar diatomic molecules are allowed to rotate within these polyatomic Rydberg molecules, we have also analyzed the impact of the Rydberg-atom-induced electric field on their rotational dynamics. We have shown that the directional properties of KRb strongly depend on the Rydberg state and on the initial rotational state of KRb forming the ultra-long range molecule. The polar molecule is signi cantly oriented and aligned if the Rydberg degenerate manifold is involved or if KRb was initially in its rotational ground state.