Fluorescence of protonated pyrene and coronene in neon matrices

Fluorescence spectra of protonated pyrene and coronene in solid neon have been observed. Laser excitation of the Sn ← S0 transitions of the cations results in an extended, vibrationally-resolved S1 → S0 fluorescence with onset at 487.8 and 695.4 nm for protonated pyrene and coronene, respectively. Vibrational assignment of the spectra has been made on the basis of the calculated frequencies of normal modes in the ground electronic state. The astrophysical relevance of the frequencies inferred for these protonated cations is discussed.