Unveiling Hidden Isomers in Ultrafast Molecular Processes using Time-resolved Photoelectron Spectroscopy*

Acetonitrile, a linear molecule, is ideal for studying photoisomerization due to its simple yet intricately bound structure, featuring both single and triple covalent bonds. Understanding the chemical processes of acetonitrile is essential for its use as a solvent in assembling DNA oligonucleotides. Theoretical calculations have been performed to determine the binding energies of different isomerization pathways in acetonitrile, revealing transient channels so far never observed. To attempt detecting these distinct channels, an IR (800 nm) pump- X-ray probe experiment was conducted at the SLAC National Accelerator Laboratory using the Linac Coherent Light Source, which operates at a high repetition rate of 8.3 kHz. X-ray photoelectron spectroscopy was used to extract the kinetic energies of the measured photoelectrons and combined with the measurement of the photon energy on a shot-to-shot basis, we can retrieve the experimental binding energies as a function of the pump-probe delay. Additionally, the technique of Spooktroscopy, which involves solving a linear regression from the experimental signal, was used to detect sub-resolution signals. These methods lead to a comprehensive understanding of the binding energy spectrum and the complex isomerization processes of acetonitrile.