Attachment of electrons with energies of 1.2 to 2 eV to ozone was found to lead to the production of O and vibrationally excited , the latter subsequently lose electrons by vibrational autodetachment. This type of electron scattering is intermediate between inelastic electron scattering and dissociative attachment. Spectra of the detached electrons have resolved vibrational structure, which can be assigned to the individual vibronic transitions, providing detailed information on the product state distribution. The absolute integral cross section for the production of in vibrational states was found to be substantial, for example at 1.7 eV it is (with an error bar of about and ). Measurements of the signal onsets permit an independent determination of the dissociation energy of ozone into O and with the result eV. Comparison of the peak width of the electrons detached by in this work with the width of peaks of resonances observed in electron- scattering indicates a moderate degree of rotational excitation in the present process.

The title compounds allow the study of the effect of the dipole moment and the energy of the lowest shape resonance on dissociative electron attachment, since both the dipole moments (2.9, 4.5, and 5.3 Debye) and the π* attachment energies (1.15, 1.98, and 2.94 eV) increase progressively along the series. An unexpected observation was made in ethylene carbonate, the molecule with the largest dipole moment, where two fragments (CO3− and C2H3O−) are formed at low energies (1–1.5 eV), well below the first π* attachment energy. We assign these bands to dissociation of a vibrationally excited dipole bound anion formed upon electron attachment. Furthermore, the number of fragments at low energies (below 5 eV) was generally found to increase with the number of oxygen atoms in the molecules, presumably because of the larger number of possible fragments with large electron affinity. Finally, “scrambling” of atoms was found in the fragmentation of ethylene carbonate even at low energies, indicating that the initially formed autodetaching anion rapidly stabilizes by sliding to sections of the potential surface where autodetachment is slow or not possible, allowing more time for chemical rearrangement. Even more “scrambling” and more fragments are found at higher energies, 6–9 eV, for all three compounds, where dissociative attachment is assigned to doubly excited Feshbach resonances.

Molecular anions have been recently detected in the denser regions of the interstellar medium. However, the chemical reactions of molecular anions with atomic species that are abundant in the ISM remain largely unexplored. This work is an experimental and computational study of CH(2)CN(-), CH(3)CHCN(-), (CH(3))(2)CCN(-), and CH(2)CHO(-) reacting with N and O atoms. In all cases the reactions of anions with O atoms exhibit larger reaction rate constants compared to the corresponding reactions with N atoms. Our study indicates that spin-forbidden reactions are the probable pathways in the reactions with N atoms, whereas spin-allowed reactions are the dominant processes in the reactions with O atoms. The major factor influencing the reaction rate constants of anions with N and O atoms is whether a spin-allowed barrierless pathway exists. The rich chemistry observed in this work provides a greater understanding of the ion-atom reaction processes, as well as some new avenues for further spin chemistry research.

A joint experimental and theoretical study of near-threshold electron-impact excitation of the 33S and 31S states in helium is reported. A high-resolution electron spectrometer is used to study integral cross sections in the energy region of the n = 3 − 5 negative-ion resonances. Photons are detected from the decay of the two states and the observed intensities are normalized to theoretical predictions using a new B-spline R-matrix (close-coupling) method that allows for non-orthogonal orbitals to improve the target description. Remarkable agreement between experiment and theory is demonstrated in both the overall energy dependence of the cross section and the fine details of a wealth of resonance structures. A detailed list of the resonances in the individual partial waves, along with their widths, is presented.