The experimental study of molecular Rydberg states has been conducted with traditional methods for generations.
However, the development of laser-based techniques such as Resonance Ionization Spectroscopy has allowed relatively easy access to these Rydberg molecules as intermediates.
[1] In 2009, a different kind of Rydberg molecule was finally created by researchers from the University of Stuttgart.
[4] This molecule was theorized in 2000 and is characterized by an electron density distribution that resembles the shape of a trilobite when plotted in cylindrical coordinates.
This new kind of atomic bond was theorized in 2002 and is characterized by an electron density distribution that resembles the shape of a butterfly.
[8] As a consequence of the unconventional binding mechanism, butterfly Rydberg molecules show peculiar properties such as multiple vibrational ground states at different bond lengths and giant dipole moments in excess of 500 debye.