The stability of the F2-ion: a model for dissociative attachment

Relativistic four-component MRCISD+Q calculations of the six lowest valence states of molecular F[Formula: see text] anion including Breit interactions

In this study, the potential energy curves of the ground and the excited states of molecular fluorine anion (F[Formula: see text]) were investigated at multireference configuration interaction (MRCISD) with Davidson size-extensivity correction (denoted as +Q) within fully relativistic four-component relativistic framework including Breit interaction. Spectroscopic constants (R_e, ω_e, ω_ex_e, ω_ey_e, D_e,D₀,B_e, α_e, β_e, γ_e ), accurate extended Rydberg analytical form and rovibrational levels for ground state X:[Formula: see text] are presented, as well as spectroscopic constants for non dissociative excited states. For most states these spectroscopic constants are presented for the first time in literature and they are of interest for experimental studies, specially regarding electron attachment of F₂. Results suggest that inclusion of relativistic effects at 4-component level and correlation effects treated at MRCISD+Q level are needed to obtain reliable results, which we report for X:[Formula: see text] ground state's R_e, ω_e and D_e the values of 1.999 Å, 391 cm^- 1 and 1.22 eV, respectively.

Intense-Field Multiple-Detachment of F2¯: Competition with Photodissociation

The competition of intense-field multiple-detachment with efficient photodissociation of F₂¯ is studied as a function of laser peak intensity. The main product channels are disentangled and characterized by 3D coincidence fragment imaging. The presented kinetic energy release spectra, angular distributions, as well as two-color pump-probe measurements allow identification of competing sequential and nonsequential mechanisms. Dissociative detachment, producing two neutral atoms (F + F), is found to be dominated by a sequential mechanism of photodissociation (F¯ + F), followed by detachment of the atomic anion fragment. In contrast, dissociative ionization (F + F⁺) shows competing contributions of both a sequential two-step mechanism as well as a nonsequential double-detachment of the molecular anion, which are distinguished by the kinetic energy released in the dissociation. Triple-detachment is found to be nonsequential in nature and results in Coulomb explosion (F⁺ + F⁺). Furthermore, the measured kinetic energy release for dissociation on the ²Σ_g⁺ state provides a direct measurement of the F₂¯ dissociation energy, D₀ = 1.26 ± 0.03 eV.

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.

Observation of p-wave threshold behavior in electron attachment to F2 molecules

Using the high resolution laser photoelectron attachment method, we demonstrate that the cross section for F- formation due to electron capture by F2(X{1}Sigma{g}{+}) molecules at very low energies exhibits p-wave threshold behavior. This finding confirms the theoretical expectation that low-energy attachment to F2 proceeds through the F2{-}(2Sigma{u}{+}) p-wave shape resonance in contrast with previous experimental claims for s-wave threshold behavior.