Ultrafast imaging of spontaneous symmetry breaking in a photoionized molecular system

The Jahn-Teller effect is an essential mechanism of spontaneous symmetry breaking in molecular and solid state systems, and has far-reaching consequences in many fields. Up to now, to directly image the onset of Jahn-Teller symmetry breaking remains unreached. Here we employ ultrafast ion-coincidence Coulomb explosion imaging with sub-10 fs resolution and unambiguously image the ultrafast dynamics of Jahn-Teller deformations of [Formula: see text] cation in symmetry space. It is unraveled that the Jahn-Teller deformation from C_3v to C_2v geometries takes a characteristic time of 20 ± 7 fs for this system. Classical and quantum molecular dynamics simulations agree well with the measurement, and reveal dynamics for the build-up of the C_2v structure involving complex revival process of multiple vibrational pathways of the [Formula: see text] cation.