Ultrafast Deep-Ultraviolet Laser Ionization Mass Spectrometry Applicable To Identify Phenylenediamine Isomers

The application of low-fragmentation mass spectrometry to identify chemicals has been recognized to be of particular importance in chemistry, biomedicine, and materials science. Utilizing a customized all-solid-state picosecond-pulsed deep-ultraviolet (DUV) laser, here we present new advances into photoionization mass spectrometry. The DUV laser ionization mass spectrometry (DUV-LIMS) results in very clean spectra pertaining to minimized structure relaxation and fragmentation under the ultrafast ionization process. Typical DUV-LIMS applications are illustrated not only for small organic molecules but also for long-chain unsaturated hydrocarbons and clusters of benzene. The unique advantages of DUV-LIMS enable us to detect and analyze confusing organic compound mixtures, indicating promising applications. DUV-LIMS is also found to be applicable in the identification of phenylenediamine isomers. An in-depth analysis of reaction dynamics is provided showing how hydrogen-atom-transfer (HAT) initiates the distinguishable photodissociation of phenylenediamines under near-resonant excitation. In particular, ortho-phenylenediamine (OPD) finds a remarkable dehydrogenation product with comparable intensity to the molecular ion peak, which is associated with the quantum tunnelling tautomers, providing new subjects for studying intramolecular noncovalent interactions.