Coulomb explosion imaging of small polyatomic molecules with ultrashort x-ray pulses

Recent multi-ion coincidence experiments with high-repetition-rate x-ray free-electron laser pulses show promise to take the decades-old Coulomb explosion imaging technique to the next level. The coincident momentum measurement of the ion fragments from molecules irradiated by ultrashort x-ray pulses enables the reconstruction of the full 3D geometries of ground-state molecules including CH3I and CH2I2. By taking such measurements at varying time delays between the optical and x-ray pulses, we can directly capture the full 3D motion of molecules excited by optical pulses. The Fourier-decomposed components of the 3D motion match well with the expected vibrational modes for both molecules.