In this Letter, we report the electronic spectrum of the allyl radical, obtained with multiconfigurational perturbation theory (MS-CASPT2). The assignment of the spectrum is in accordance with experiment to within 0.2 eV. We have computed the complete first Rydberg series and the beginning of the second Rydberg series. A new valence-excited B-2(1) state has been found which has hitherto been hidden by Rydberg transitions. A rationalisation of the electronic spectrum is provided in terms of resonance forms in ground and excited states. This model shows that while a multiconfigurational wavefunction is necessary to qualitatively model the system, the large ionic character of the valence electronic states makes an accurate treatment of the dynamical correlation necessary for a quantitative description of the spectrum. (C) 2003 Elsevier B.V. All rights reserved.
Aquilante, F., Kepp, K. P., & Roos, B. O. (2003). The allyl radical revisited: A theoretical study of the electronic spectrum. Chemical Physics Letters, 380(5-6), 689-698. https://doi.org/10.1016/j.cplett.2003.09.079