Imaging Three-Dimensional Molecular Structure and Dynamics with Multiparticle Covariance and Cumulant Coulomb...

Area of Science:

• Chemical Physics
• Molecular Imaging
• Ultrafast Dynamics

Background:

• Coulomb explosion imaging (CEI) reconstructs molecular geometry from fragment ion momenta.
• Understanding molecular dynamics requires precise structural information.

Purpose of the Study:

• To extract three-dimensional (3D) structural information from X-ray-induced Coulomb explosion of tert-butyl iodide.
• To demonstrate covariance and cumulant analysis for molecular imaging.

Main Methods:

• Site-selective ionization of tert-butyl iodide at the iodine 4d edge using femtosecond soft X-ray pulses.
• Three-body covariance and four-body cumulant analysis of fragment ions.
• Comparison with point-charge simulations.

Main Results:

• Complete dissociation channels were isolated by correlating ionic fragments.
• Subtle structural changes, including umbrella-type motion of the alkyl chain, were revealed.
• Simulations showed close agreement with experimental data, validating the approach.

Conclusions:

• Covariance/cumulant mapping is a powerful strategy for imaging complex 3D molecular structures.
• This method paves the way for time-resolved CEI to capture ultrafast structural dynamics.