Unraveling the Spectroscopy of the Phenalenyl Radical.

Jet-cooled excitation spectra of the phenalenyl radical are obtained using resonance enhanced multiphoton ionization. The excitation spectra reveal previously unobserved transitions, up to 17,000 cm^-1 above the D₁ origin, including transitions to electronically forbidden A₂ ^″ electronic states. A quasi-diabatic approach is applied to construct a vibronic Hamiltonian, including both Jahn-Teller and pseudo-Jahn-Teller interactions, between seven excited electronic surfaces. This is employed to calculate the electronic excitation spectrum of the phenalenyl radical in its entirety, providing vibronic assignments and spectral parameters to help decode the spectroscopy of this key radical.