IR and UV Spectroscopy of Vapor-Phase Jet-Cooled Ionic Liquid [emim]⁺[Tf₂N]⁻: Ion Pair Structure and Photodissociation Dynamics

Small gas-phase clusters (ion pairs) of the ionic liquid [emim]⁺[Tf₂N]⁻ have been generated in a supersonic expansion. Clusters are investigated via UV photofragmentation and time-of-flight mass spectrometry. Spectra between 42 000 and 45 000 cm^–1 reveal dynamical branching between direct dissociation of the ion pair to the cation and anion and to radical species. The IR spectrum between 2800 and 3200 cm^–1 was measured by action spectroscopy. Multiple conformations of the ion pair are found to be present in the molecular beam, leading to broad spectral features, further complicated by hydrogen bonding and Fermi resonances. The measured and theoretical spectra compare well, and the jet-cooled ion pair structures present in the molecular beam are strongly hydrogen bonded “stacked” conformers