Ultrafast imaging of spontaneous symmetry breaking in a photoionized molecular system

Abstract

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 $${{\rm{CH}}}_{4}^{+}$$ CH 4 + cation in symmetry space. It is unraveled that the Jahn-Teller deformation from C3v to C2v 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 C2v structure involving complex revival process of multiple vibrational pathways of the $${{\rm{CH}}}_{4}^{+}$$ CH 4 + cation.

Multi-mass velocity map imaging study of the 805 nm strong field ionization of CF3I

“…Determining the fragment ion velocities and momenta using, for example, coincidence velocity map imaging (VMI) methods or VMI in conjunction with covariance analysis methods offers a route to determine static molecular structures, [10][11][12] to distinguish isomers [13][14][15][16][17][18] and enantiomers, 19 to explore the fragmentation dynamics of multiply charged cations 20 and, in appropriately-designed ultrashort laser pulse pump-probe experiments, to follow the time-evolving structure and/or the fragmentation of photoexcited small molecules [21][22][23] and ions. [24][25][26] The present study explores the fragmentation dynamics of multiply charged CF 3 I Z+ ions formed by non-resonant NIR SFI. Each excitation pulse creates a distribution of multiply-charged parent cations, which display Z-dependent explosion dynamics.…”

Molecular photodissociation dynamics revealed by Coulomb explosion imaging

“…49 Such experiments have, for example, recently allowed real-time studies of the Jahn-Teller driven distortions of the CH 4 + cation. 50 Fig. 2 provides an impressive recent illustration, where CE methods have been used to reveal the momenta (and thus, after due processing, the positions) of all atoms within the 2-iodopyridine molecule.…”

Femtosecond symmetry breaking and coherent relaxation of methane cations via x-ray spectroscopy

“…Coulomb explosion experiments by Li et al . ( 22 ) probed the dynamics of CH 4 + by recording the photofragments after interaction with two time-delayed strong-field 800-nm pulses, but temporal resolution was limited by the 25-fs pulses used as pump and probe. Furthermore, their use of a multicycle pump pulse led to several additional photoproducts from higher-energy fragmentation pathways that compete with JT distortions.…”