A theoretical study of the 21Ag ← 11Ag two-photon transition and its vibronic band in trans-stilbene

The two-photon spectrum of the 2¹A_g ← 1¹A_g transition in trans-stilbene has been calculated at the complete active space self-consistent field (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and final states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active π orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest π orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck-Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force fields of both the initial and final states, at the CASSCF level of theory. The results are in agreement with experiment.     

A density functional study of plutonyl trifluoroacetone complexes in the gas phase and in solution

The results of a density functional study on a plutonyl compound with two trifluoroacetone ligands are presented. Several conformations of the complex have been examined, namely the structure in which the two ligands are in a cis conformation one with respect to the other, in a trans conformation one with respect to the other, and the structure in which the two ligands lie on the same plane. The calculations have been carried out at the local density approximation level of theory. The relative energies of the conformers have been determined and their geometries have been optimized in the gas phase and in an organic solution. The liquid-state environmental effects are included via a simple cavity model and by using the self-consistent reaction field method. This study shows that the trends in stability of the different conformers in the gas and liquid phases are similar and that the most stable conformer has a cis structure.