Electronic Spectroscopy of Resonantly Stabilized Aromatic Radicals: 1‑Indanyl and Methyl Substituted Analogues

The gas-phase electronic spectra of two resonantly stabilized radicals, 1-indanyl (C<sub>9</sub>H<sub>9</sub>) and 1-methyl-1-indanyl (C<sub>10</sub>H<sub>11</sub>), have been recorded in the visible region using a resonant two-color two-photon ionization (R2C2PI) scheme. The D<sub>1</sub>(A″) ← D<sub>0</sub>(A″) origin bands of 1-indanyl and 1-methyl-1-indanyl radicals are observed at 21157 and 20565 cm<sup>–1</sup>, respectively. The excitation of a′ vibrations in the D<sub>1</sub> state is observed up to ∼1500 cm<sup>–1</sup> above the origin band in both cases. The experimental assignments are in agreement with DFT and TD-DFT calculations. The R2C2PI spectrum recorded at <i>m</i>/<i>z</i> = 131 amu (C<sub>10</sub>H<sub>11</sub>) features three additional electronic transitions at 21433, 21369, and 17989 cm<sup>–1</sup>, which are assigned to the origin bands of 7-methyl-1-indanyl, 2,3,4-trihydronaphthyl, and methyl-4-ethenylbenzyl radicals, respectively.