Different Time Scales in the Dissociation Dynamics of Core-Excited CF_{4} by Two Internal Clocks.

Fragmentation processes following C 1s→lowest unoccupied molecular orbital core excitations in CF_{4} have been analyzed on the ground of the angular distribution of the CF_{3}^{+} emitted fragments by means of Auger electron-photoion coincidences. Different time scales have been enlightened, which correspond to either ultrafast fragmentation, on the few-femtosecond scale, where the molecule has no time to rotate and the fragments are emitted according to the maintained orientation of the core-excited species, or dissociation after resonant Auger decay, where the molecule still keeps some memory of the excitation process before reassuming random orientation. Potential energy surfaces of the ground, core-excited, and final states have been calculated at the ab initio level, which show the dissociative nature of the neutral excited state, leading to ultrafast dissociation, as well as the also dissociative nature of some of the final ionic states reached after resonant Auger decay, yielding the same fragments on a much longer time scale.

Theoretical investigations on CaO ions: vibronic states and photoelectron spectroscopy.

The low-lying electronic states, X(2)Π and A(2)Σ(+) of CaO(+) and X(2)Σ(+) and A(2)Π of CaO(-), have been determined at the MRCI+Q level of theory with the aug-cc-pV5Z(O) and cc-pCV5Z(Ca) basis sets. The two states of CaO(+) are close within <0.1 eV and coupled via spin-orbit effect. The X(2)Σ(+) and A(2)Π states of CaO(-) are energetically separated by <1 eV such that the first excited state is close to the electronic ground state of neutral CaO and unstable with respect to electron detachment. Using the potential energy curves and the spin-orbit coupling terms, the vibronic energy levels of these ions have been determined. The ionization energy and the electron affinity of CaO are calculated at 6.79 and 0.79 eV, respectively. The photoelectron spectra of CaO(-) and CaO have also been simulated.

Theoretical study of the predissociation of the A2Π state of ZnF including quasi-diabatisation of the spin-orbit coupling.

The excited (2)Π electronic states of ZnF have been diabatized in order to simulate the (2)Π â† X(2)Σ(+) vibronic spectrum using a wavepacket propagation technique. The spin-orbit coupling functions within the (2)Π states and between the (2)Π and B(2)Σ(+) states have also been diabatized, as well as the dipole and transition moment functions. As the adiabatic electronic (2)Π states are strongly multi-configurational, the quasi-diabatisation scheme was based on the electronic wavefunction overlap along the reaction coordinate. The procedure leads to a repulsive (2)Π state reaching the first dissociation limit, Zn((1)S(g)) + F((2)P(u)), and a bound one associated with the second limit, Zn((3)P(u)) + F((2)P(u)). The adiabatic electronic potentials and coupling functions have been determined at the multi-reference-configuration-interaction level of theory. The vibrational energies and the spin-orbit splittings are in agreement with early experimental data. The wavepacket propagation approach, coupled with a Prony analysis, allowed also to analyze the resonances and the bound vibronic states of the (2)Π manifold. The (2)Π â† X(2)Σ(+) vibronic spectra have been determined for Ω = 1/2 and 3/2 originating to the v'' = 0 level of the X(2)Σ(+) state.

A theoretical spectroscopic study of HeI and HeBr.

Highly accurate potential energy functions for the HeI and HeBr molecules have been calculated using an ab initio treatment that included basis set extrapolation to the complete basis set, as well as spin-orbit coupling in the ground 2sigma+ and first 2pi excited doublet states. The rovibronic bound state energies and resonance lifetimes were also evaluated by a Prony analysis of the autocorrelation function of the evolving wave packet.