Shape-resonance-induced long-range molecular Rydberg states

Edward L Hamilton, Chris H Greene, H R Sadeghpour
2002 Journal of Physics B: Atomic, Molecular and Optical Physics  
When an excited atomic electron interacts with a neutral perturbing atom or molecule that possesses a shape resonance, it generates a characteristic class of Born-Oppenheimer potential curves that rise with internuclear distance. We document this effect, and predict the existence of a diverse class of stable, strongly bound atom-atom and atom-molecule states that result from this phenomenon. For the specific case in which Rb is the perturbing atom, we show that such states should be observable
more » ... ould be observable in the spectroscopy of an ultracold gas or condensate. M This article features online multimedia enhancements When an atom in a low-lying excited state or a Rydberg state is brought near a ground state atom or molecule, much of the interaction derives from simple electron scattering off the ground state species. This picture was developed in a classic paper by Fermi [1] to describe pressure shifts of atomic Rydberg spectral lines. In a high Rydberg state, the electron kinetic energy is so low that the electron-perturber scattering is primarily s-wave, and in that case the main physics is carried by the s-wave scattering length. A recent study [2] showed that, in an ultracold gas, the negative 3 S-wave scattering length can produce a new type of ultralong-range molecule with unusual properties. The purpose of this letter is to predict the existence of a new and very different class of long-range molecular states that arise when the electron-perturber scattering exhibits a shape resonance. Electron-atom or electron-molecule shape resonances have been studied extensively in their own right, but their manifestation as features in a Born-Oppenheimer molecular potential curve or surface has apparently not been elucidated. Among the properties that we predict are: (i) much stronger binding energies than were predicted for other predicted classes of long-range Rydberg states; (ii) in some cases, the existence of large permanent electric dipole moments. Creation, storage and manipulation of cold dilute atomic gases by laser and magnetic cooling have spawned novel and high-precision spectroscopic analyses of atomic and molecular 0953-4075/02/100199+08$30.00
doi:10.1088/0953-4075/35/10/102 fatcat:qi5oore65zeqzngoxsuekvmgly