Single photon infrared emission spectroscopy of the gas phase pyrene cation: support for a polycyclic aromatic hydrocarbon origin of the unidentified infrared emission bands.

We report the first observation of infrared emission from a gaseous ionic polycyclic aromatic hydrocarbon (PAH), the pyrene cation, over the range of wavelengths spanned by the ubiquitous interstellar unidentified infrared emission bands (UIRs). The complete set of pyrene cation IR emissions is observed, with relative intensities consistent with astrophysical observations, supporting the proposal that ionized PAHs are major contributors to the UIR bands. Additionally, unidentified features possibly arising from dehydrogenated PAH species are noted in the spectrum.