Valence and n=3 Rydberg excited states of the allyl radical:: A theoretical study using spin-coupled valence-bond theory

Three and seven-electron ab initio spin-coupled (SC) calculations have been performed on the allyl radical. The global minimum energy ground state corresponds to an antipair solution, while a local minimum 1.3 mhartree above in energy corresponds to a localized (VB) description of the radical. A two-configuration spin-coupled valence bond (SCVB) calculation shows that the antipair solution is dominant over the localized solution. Three-electron multireference (MR) SCVB calculations on the valence and n = 3 Rydberg states of the allyl radical were then performed using as starting point the antipair solution.