The electronically excited states of RDX (hexahydro-1,3,5-trinitro-1,3,5- triazine): Vertical excitations

The RDX molecule, hexahydro-1,3,5-trinitro-1,3,5-triazine, is a key component for several energetic materials, which have important practical applications as explosives. A systematic study of the electronic excited states of RDX in gas phase using time-dependent density functional theory (TDDFT), algebraic diagrammatic construction through second order method [ADC (2)], and resolution of the identity coupled-cluster singles and doubles method (RI-CC2) was carried out. Transition energies and optical oscillator strengths were computed for a maximum of 40 transitions. RI-CC2 and ADC (2) predict a spectrum shaped by three intense π- π* transitions, two with charge transfer and one with localized character. TDDFT fails in the description of the charge transfer states. The low-energy band of the experimental UV spectrum of RDX is assigned to the first charge transfer state. Two alternative assignments of the high-energy band are proposed.