Orbiting Orbitals: Visualization of Vibronic Motion at a Conical Intersection

Abstract

The Jahn-Teller (JT) active unpaired electron of single metalloporphyrin radical anions is imaged through scanning tunneling microscopy. It is demonstrated that the electron is delocalized over the porphyrin macrocycle and its topographic image is determined by vibronic motion: the orbital of the electron adiabatically follows the zero-point pseudorotation of skeletal deformations. Transformation of the polar graphs of the observed images allows visualization of the adiabatic vibrational density to which the electron is coupled. The vibronic potential at the conical intersection is visualized and the half-integer angular momentum characteristic of the Berry phase is revealed in the radial function of the electron. The measurements underscore the economy of Jahn-Teller dynamics: small atomic displacements (∼10(-1) Å) determined by weak interactions (∼10 meV) control the motion of the electron on a 10 Å scale and determine the molecular shape and function.