Temporal- and angular-resolved photoionization experiments are essential for probing the geometric configuration and electronic state evolution of atoms and molecules, which requires measuring the full spatial angular distributions of electrons and ions in free electron laser (FEL) experiments. Here, we present the first experimental results from the composite velocity imaging spectrometer (CpVMI) on the Shanghai soft X-ray free electron laser facility (SXFEL). The study demonstrates its ability to capture energy and angular information of electrons and ions with high resolution and full solid-angle collection.

Krypton (Kr) atoms and carbon tetrachloride (CCl₄) molecules are ionized using FEL pulses at 263.8 eV. Electron momentum images are recorded with an Andor Zyla 4.2 PLUS camera, and ion time-of-flight mass spectra and momentum distributions are acquired using a TPX3CAM. For Kr, the electron spectrum contains peaks from 3p, 3d, and 4p photoionization, as well as the Auger electrons from 3d and 3p levels. The measured anisotropy parameters (β) of these electrons show good agreement with previous theoretical Hartree-Fock calculations. The ion abundance in the time-of-flight mass spectra of Kr is consistent with the ratio derived from the intensities of the corresponding photoelectron peaks.

For CCl₄, the electron spectrum contains Cl 2p photoelectrons, 2p Auger electrons, and valence-shell photoelectrons, with their angular distribution parameters also aligning with theoretical predictions. The TPX3CAM can directly measure the momenta of fragment ions without the need of inverse Abel transformation. By integrating the high-resolution flight time mass spectrometry and momentum imaging data obtained from TPX3CAM, we successfully visualize and analyze the key photodissociation pathways of CCl₄ molecules under the action of soft X-ray FEL. In particular, it can distinguish between direct two-body dissociation and multi-step dissociation processes, and observe the unique angular distributions and kinetic energy release characteristics of different dissociation channels.

In conclusion, the experimental results clearly show that the CpVMI fully meets the technical requirements for FEL user experiments in terms of energy, angular distribution, and momentum measurement, providing a platform for FEL light-induced dynamics research. Future enhancements, including improved light focusing and the use of supersonic molecular beams, are expected to further improve the performance of the instrument.