Isotope and Temperature Effects on the Electronic Spectra of Large Carbonaceous Molecular Ions of Interstellar Relevance

The electronic spectra of isotopologues of protonated coronene in the gas phase were measured at a vibrational and rotational temperature of similar to 10K in a 22-pole ion trap. The (1) (1)A'<- X(1)A' transition of these polycyclic aromatic hydrocarbon cations with one to three carbon-13 have origin band maxima that blue-shift successively by 0.03nm. All isotopologues show distinct vibrational structure in the (1) (1)A' state. These results are compared with the effect of C-13 substitution on the near infrared electronic absorptions of C-60(+). The (1) (1)A <- X(1)A electronic transition of monodeuterated coronene was also recorded and its origin band is red-shifted to that of protonated coronene by 0.8nm. The implications for astronomical observations are considered.