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Single-Photon Infrared Emission Spectroscopy of Gaseous Polycyclic Aromatic Hydrocarbon Cations: A Direct Test for Proposed Carriers of the Unidentified Infrared Emission Bands

We describe the measurement of infrared emission from excited gas-phase polycyclic aromatic hydrocarbons (PAHs) cations by an electron-impact ion beam reflectron system coupled to our "single-photon infrared emission" (SPIRE) spectrometer. This experiment provides for direct comparison of laboratory infrared emission spectra of gaseous ionized PAHs with the "unidentified infrared emission bands" (UIRs), the origin of which is still debated. We present results for the pyrene cation (C16H10+) and the dehydrogenated pyrene cations (C16H8+ and C16H6+) showing general agreement between the corresponding SPIRE bands and UIR features, although it is not a detailed match. We also discuss possible contributions from the pyrene dimer cation (C16H10)2+.