Single photon infrared emission spectroscopy of the gas phase pyrene cation: Support for a polycyclic aromatic hydrocarbon origin of the unidentifiedinfrared emission bands

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