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Laser-ablated group 6 metal atoms react with NF3 and PF3 to form the simple lowest energy N MF3 and P=MX3 products, and this investigation has been extended to AsF3. Mo and W atoms react with AsF3 upon excitation by laser ablation or UV irradiation to form stable trigonal As MF3 terminal arsenides. These molecules are identified by comparison of the closely related infrared spectra of the analogous phosphide species and with frequencies calculated by density functional theory and multiconfigurational second order perturbation theory (CASSCF/CASPT2). Computed CASSCF/CASPT2 triple bond lengths for the As MoF3 and As WF3 molecules are 2.240 angstrom and 2.250 angstrom, respectively. The natural bond orders calculated by CASSCF/CASPT2 decrease from 2.67 to 2.60 for P MoF3 to As MoF3 and from 2.74 to 2.70 for P WF3 to As WF3 as the arsenic valence orbitals are less effective than those of phosphorus in bonding to each metal atom and the larger metal orbital size becomes more compatible with the arsenic valence orbitals. The Cr atom reaction gives the arsinidene AsF=CrF2 product instead of the higher energy As CrF3 molecule as the Cr (VI) state is not supported by the softer pnictides. (Less)

New basis sets of the atomic natural orbital (ANO) type have been developed for the main group and rare gas atoms. The ANO's have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive and negative ions, and the dimer at its equilibrium geometry. Scalar relativistic effects are included through the use of a Douglas−Kroll Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies, electron affinities, and excitation energies for all atoms and the ground-state potentials for the dimers. These calculations include spin−orbit coupling using the RASSCF State Interaction (RASSI-SO) method. The spin−orbit splitting for the lowest atomic term is reproduced with an accuracy of better than 0.05 eV, except for row 5, where it is 0.15 eV. Ionization energies and electron affinities have an accuracy bett...

The results of a theoretical study of the ground state, 1(1)A(g), and of the lowest B-1(u) states of trans-stilbene are presented. The vertical and adiabatic excitation energies of the lowest B-1(u) states have been computed using multiconfigurational SCF theory, followed by second-order perturbation. theory. It is shown that the two lowest excited states are separated by a small energy gap in the Franck-Condon region. They are the 1(1)B(u), characterized by the HOMO-->LUMO single excitation substantially localized on the ethylenic moiety, and the 2(1)B(u), formed by a combination,of one electron excitations localized mainly on the benzene rings. The most intense transition is found to be the lowest in energy when the interaction between different states is included at the level of second-order perturbation theory. The vibronic structure of emission and absorption spectra of the two lowest B-1(u) states have been determined within the Franck-Condon approximation. The spectrum calculated for the 1(1)B(u) state agrees with the experimental spectrum, while the low intensity band computed for the 2(1)B(u) state has no experimental counterpart. It is concluded that this band is buried in the strong 1(1)B(u) absorption and therefore not observed. (Less)

The structure and vibrational frequencies of the UO[2] molecule have been determined using multiconfigurational wave functions (CASSCF/CASPT2), together with a newly developed method to treat spin−orbit coupling. The molecule has been found to have a (5f[phi])(7s), [3]Φ[u], Ω = 2 ground state with a U−O bond distance of 1.77 Å. The computed antisymmetric stretching σu frequency is 923 cm[-1] with a 16/18 isotope ratio of 1.0525 which compares with the experimental values of 915 cm[-1] and 1.0526, respectively. Calculations of the first adiabatic ionization energy gave the value 6.17 eV, which is 0.7 eV larger than the currently accepted experimental result. Reasons for this difference are suggested.