PNNL

Abstract

(12/12)CASPT2, (16/14)CASPT2, B3LYP, and CCSD(T) calculations have been carried out on 1,8-Naphthoquinone (1,8-NQ), in order to predict the low-lying electronic states and their relative energies in this non-Kekulé quinone diradical. CASPT2 predicts a 1A1 ground state, with three other electronic states – 3B2, 3B1, and 1B1 – within about 10 kcal/mol of the ground state in energy. In contrast, CCSD(T) finds 3B2 to be the ground state, with 1A1 slightly higher in energy. Based on the comparisons of the singlet-triplet energy differences (?EST), calculated by CASPT2 and by CCSD(T) for two other non-Kekulé quinone diradicals, with the experimental values measured, by negative ion photoelectron spectroscopy (NIPES), it is predicted that NIPES experiments on 1,8-NQ•– will find that 1,8-NQ is a diradical with a singlet ground state.