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 (C₉H₉) and 1-methyl-1-indanyl (C₁₀H₁₁), have been recorded in the visible region using a resonant two-color two-photon ionization (R2C2PI) scheme. The D₁(A″) ← D₀(A″) origin bands of 1-indanyl and 1-methyl-1-indanyl radicals are observed at 21157 and 20565 cm^–1, respectively. The excitation of a′ vibrations in the D₁ state is observed up to ∼1500 cm^–1 above the origin band in both cases. The experimental assignments are in agreement with DFT and TD-DFT calculations. The R2C2PI spectrum recorded at m/z = 131 amu (C₁₀H₁₁) features three additional electronic transitions at 21433, 21369, and 17989 cm^–1, which are assigned to the origin bands of 7-methyl-1-indanyl, 2,3,4-trihydronaphthyl, and methyl-4-ethenylbenzyl radicals, respectively.