Complex configuration interaction calculations of the cross section for the dissociative electron attachment process e(-) + F2 → F2(-) → F + F(-) using the complex basis function method.

The F(2)(-) molecule and the corresponding dynamic processes dealing with electron scattering on the neutral F(2) species have been the subject of many theoretical and experimental investigations in the past. In the context of the Born-Oppenheimer approximation, one of the best theoretical descriptions of the electronic states involves the use of complex basis functions together with configuration interaction (CI) methods. In this work, multireference CI calculations using the complex basis function method have been carried out for the autoionizing ground state of the F(2)(-) molecule. Potential curves and vibrational levels have been obtained for the ground and various excited states of both F(2) and F(2)(-), as well as the variation of the line width of the anionic ground state for the bond distance region in which it is metastable. Cross sections for the dissociative electron attachment process e(-) + F(2) → F(2)(-) → F + F(-) have also been computed within the framework of the boomerang model, and good agreement with available experimental data has been found. In addition, some calculations for the process of vibrational excitation are included which also give good agreement with experiment.

Use of complex configuration interaction calculations and the stationary principle for the description of metastable electronic states of HCl(-).

The complex multireference single- and double-excitation configuration interaction method has been employed to compute potential curves for the anion of the hydrogen chloride molecule. First, conventional CI calculations with real basis functions have been carried out to determine the potential curves of both HCl and its anion over a large range of internuclear distance. It is shown that adding basis functions with very small exponents leads to sharply avoided crossings for the HCl(-) potentials that greatly complicate the search for resonance states thought to be responsible for features observed in electron collision experiments. By limiting the number of such diffuse-type functions it is possible to describe resonance states at a highly correlated level and still account for their interaction with the continuum in which they are embedded. In the present study of the HCl(-) anion the complex basis function technique of Moiseyev-Corcoran and McCurdy-Resigno is employed to calculate the energy positions and line-widths of the resonance states. Two states of (2)Sigma(+) symmetry are calculated which have potentials that have significantly different shapes than that of the neutral ground state and thus contribute to the cross section for vibrational excitation of the neutral HCl molecule induced by low-energy electron collisions. The lower of these (1 (2)Sigma(+)) correlates smoothly with the bound anionic ground state at large internuclear distances and is seen to be responsible for the sharp peaks observed in the low-energy region of the spectrum. The upper state (3 (2)Sigma(+)) has a much larger bond length and is assigned to the broad bands observed with a maximum in the 2.5-3.0 eV range. The present calculations thus stand in contradiction to earlier claims that the above peaks are caused by so-called virtual states without a definite autoionization lifetime.

Complex multireference configuration interaction calculations employing a coupled diabatic representation for the 2Pi(g) resonance states of N2(-).

Complex multireference configuration interaction calculations have been carried out for the lowest resonance states of (2)Pi(g) symmetry of the N(2)(-) molecule. It is shown that there is a forbidden crossing between the two lowest roots of this symmetry and that a satisfactory calculation of vibrational levels and cross sections therefore requires inclusion of both states and the coupling between them. A diabatic representation for the two (2)Pi(g) states was determined and vibronic calculations of the cross sections for vibrational excitation were carried out with a two-dimensional complex variational program.

Complex self-consistent field and multireference single- and double-excitation configuration interaction calculations for the 2Pi(g) resonance state of N2-.

Self-consistent field and multireference single- and double-excitation configuration interaction calculations employing the complex basis function technique are carried out for the (2)Pi(g) resonance state of the N(2) (-) molecule as well as several other anionic resonance states in the neighboring energy region. The results of calculations employing the same method for the (1)S (2s(2)) state of the He atom and the (1)Sigma(g) (+) (sigma(u) (2)) state of the H(2) molecule are found to be in good agreement with those of earlier work. The present theoretical treatment has succeeded for the first time in satisfying the rigorous criterion of the complex variational principle in computing the N(2) (-) resonance states, namely, a cusp in the plots of real versus imaginary components of the corresponding complex energies has been located at each internuclear distance. On this basis, it is found that the open-shell orbital in the lowest-energy adiabatic N(2) (-) resonance state of (2)Pi(g) symmetry changes its character from quite compact at large internuclear distance to relatively diffuse for r<2.3a(0). This is in contrast to all previous theoretical treatments of this system that have not rigorously satisfied the complex variational principle in their determination of this wave function.