Fano-Feshbach formalism applied to the calculation of autoionization widths through analytic continuation.

A method to calculate the autoionization width from a discretized pseudo-spectrum is proposed. This method relies on an analytic continuation of Green's function within the Fano-Feshbach formalism. The pseudo-spectrum is obtained at the multireference configuration interaction level in a square-integrable basis set, commonly found in quantum chemistry software. Few states around the desired resonance are needed to perform the analytic continuation. This method was applied to atomic (He and Ne) and molecular (HF and benzene) systems, and the results for the autoionization width show good agreement with the available theoretical and experimental values.

Electron-molecule collisions with explicit rovibrational resolution at MRCI level and using even tempered basis sets.

A method for calculating the generalized oscillator strengths (GOSs) and differential cross section (DCS) with vibration and rotation resolution is presented. The importance of accounting for the rotational contribution is to be emphasized since it has not previously been considered in GOS calculations. Although largely neglected due to its small effect on various properties, the rotational resolution proved to be fundamental in the study of certain phenomena, such as the interference between rotational states in a molecule. As the general goal of this work is to obtain theoretical values comparable to high resolution experiments, special care was taken on the calculation of the electronic part of the scattering amplitude, particularly in what concerns the choice of the atomic basis set. Accordingly, even-tempered basis sets have proved to lead to good results. The helium atom was taken as a model system for this aspect of the problem. Then, GOS and DCS, for explicit vibrational and rotational transitions, were calculated for hydrogen and nitrogen molecules. For higher accuracy, a non-Franck-Condon approach was used to obtain transitions involving vibrational states. The resultant values have shown good agreement with the available experimental data.

Generalized oscillator strengths of carbon disulfide calculated by multireference configuration interaction.

Transition energies and generalized oscillator strengths (GOSs) for transitions up to 6.3 eV of carbon disulfide were calculated at the multireference configuration interaction level. It is shown that the consideration of the vibronic coupling mechanism is essential to establish not only a quantitative but also a qualitative profile of the GOS, as a function of the momentum transferred, for the dipole forbidden transitions (Σg+1→1Σu - and Σg+1→1Δu). For the dipole allowed Σg +→Σu + transition, the calculated GOS is in good agreement with the available experimental data.

Experimental evidence of twin fast metastable H(2(2)S) atoms from dissociation of cold H2 induced by electrons.

We report the direct detection of two metastable H(2^{2}S) atoms coming from the dissociation of a single cold H(2) molecule, in coincidence measurements. The molecular dissociation was induced by electron impact in order to avoid limitations by the selection rules governing radiative transitions. Two detectors, placed close to the collision center, measure the neutral metastable H(2(2)S) through a localized quenching process, which mixes the H(2^{2}S) state with the H(2^{2}P), leading to a Lyman-α detection. Our data show the accomplishment of a coincidence measurement which proves for the first time the existence of the H(2(2)S)-H(2(2)S) dissociation channel.