Excitation spectra of large jet-cooled polycyclic aromatic hydrocarbon radicals: 9-Anthracenylmethyl (C15H11) and 1-pyrenylmethyl (C17H11)

The 9-anthracenylmethyl (C15H11) and 1-pyrenylmethyl (C17H11) radicals were identified by a combination of mass-resolved laser spectroscopy of a jet-cooled electrical discharge and quantum chemical methods. The 9-anthracenylmethyl radical was found to exhibit an origin band at 13757 cm-1, with vibrational structure observed in a1 modes, and even quanta of b1 and a2 modes. The 1-pyrenylmethyl radical was found to exhibit an origin band at 13 417 cm-1, with a more complex vibrational structure as compared to 9-anthracenylmethyl, on account of its lower symmetry and larger size. The origin bands of these species were predicted to within 250 cm-1 by fitting a linear relationship between observed origin wavelengths of similar chromophores and the calculated TD-B3LYP transition energies. A refined fit including the title radicals provides estimated absorption energies for the larger 2-perylenylmethyl and 6-anthanthrenylmethyl species of 1.44 and 1.41 eV, respectively, with an estimated error of 30 meV. © 2013 American Chemical Society.