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The two lowest bands, 1 B 2u and 1 B 1u , of the electronic spectrum of the benzene molecule have been studied theoretically using a new method to compute vibronic excitation energies and intensities. The complete active space ͑CAS͒ self-contained field ͑SCF͒ method ͑with six active -orbitals͒ was used to compute harmonic force field for the ground state and the 1 B 2u and 1 B 1u electronic states. A linear approximation has been used for the transition dipole as a function of the nuclear displacement coordinates. Derivatives of the transition dipole were computed using a variant of the CASSCF state interaction method. Multiconfigurational second-order perturbation theory ͑CASPT2͒ was used to obtain absolute excitation energies ͑12 active -orbitals͒. The results show that the approach works well. Vibrational progressions are well described in both bands and intensities, and energies are in agreement with experiment, in particular when CASPT2 derived geometries are used. One interesting result is that computed vertical energies fall about 0.1 eV on the high energy side of the band maximum.

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ABSTRACT:We present a theoretical study on the dissociation reaction of N 8 azapantalene to four N 2 molecules. The process proceeds via isomerization of N 8 azapentalene to N 8 azidopentazole, which then dissociates directly into four nitrogen molecules. The calculations have determined the relative energies of the two isomers and the two transition states involved in the dissociation process. The results show azidopentazole to be 13 kcal/mol more stable than azapentalene. The barrier to dissociation into four N 2 molecules is computed to be 19 kcal/mol. It is concluded that N 8 is not stable enough to be considered as a candidate for a high-energy density material. The calculations have been carried out using multiconfigurational self-consistent field and second-order perturbation theory.