The Air Force has a pressing need to find new means of spacecraft propulsion, enabling cheaper, safer, more efficient maneuvering on orbit. Ionic liquids are a potential replacement for  hydrazine in hypergolic combustion propellant systems and for xenon in electric propulsion systems. However, both applications require considerable further development, leading us to study the fundamental structural and optical properties of candidate systems. Our benchmark measurements will provide validation of theoretical models of all types, from ab initio methods up to codes describing full thruster plumes. Using standard supersonic jet time-of-flight spectroscopy techniques, we have measured the ultraviolet and infrared spectra of ion pairs of the only space-qualified ionic liquid, [emim][Tf2N]. The ultraviolet photodissociation spectrum, though broad and essentially featureless, reveals rich underlying photodynamics involving both single- and multiphoton excitations and a wealth of interacting excited states. The infrared spectrum and DFT calculations establish the structure as one in which the cation and anion are stacked on top of one another rather than sitting in the same plane, answering a long-standing question in this field. The complexity of the infrared spectrum and its behavior under varying jet temperatures indicates the presence of multiple conformations and likely contributions from Fermi resonance.

Ion pair structure and photodissociation dynamics of ionic liquid [emim][Tf<sub>2</sub>N]

248th National Meeting (2014)

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Ion pair structure and photodissociation dynamics of ionic liquid [emim][Tf2N]

Ion pair structure and photodissociation dynamics of ionic liquid [emim][Tf₂N]