Unveiling hidden isomers in ultrafast molecular processes using time-resolved X-ray photoelectron spectroscopy with a free electron laser*

Photoisomerization is a crucial mechanism in both biological and chemical processes, making it an essential phenomenon to study. Acetonitrile is an ideal candidate for investigating photoinduced isomerization due to its simple linear structure and the presence of both single and triple covalent bonds. Theoretical calculations have explored the different isomerization pathways in acetonitrile, revealing both cyclic and unique linear isomers that have not yet been observed. To detect these isomers, we conducted an experiment using a strong infrared (800 nm ~ 1.55eV) pump and a femtosecond X-ray (525eV) probe from the Linac Coherent Light Source operating at a high repetition rate of 8.3 kHz. At various pump-probe delays, we measured the photoelectron kinetic energy spectra and the X-ray spectra. A correlation analysis method, spectral-domain ghost imaging, was employed to improve resolution in the time-resolved binding energy spectrum of the infrared-pumped acetonitrile. We will present our work which incorporates these multiple techniques to allow a thorough understanding of the complex isomerization pathways of acetonitrile.