Anionic states of C6Cl6 probed in electron transfer experiments.

This is the first comprehensive investigation on the anionic species formed during collisions of fast neutral potassium (K) atoms with neutral hexachlorobenzene (C6Cl6) molecules in the laboratory frame range from 10 up to 100 eV. In such ion-pair formation experiments we also report a novel K+ energy loss spectrum obtained in the forward scattering giving evidence of the most accessible electronic states. The vertical electron affinity of (-3.76 ± 0.20) eV has been obtained and assigned to a purely repulsive transition from the C6Cl6 ground state to a state of the temporary negative ion yielding Cl- formation. These experimental findings are also supported by state-of-the art theoretical calculations on the electronic structure of C6Cl6 in the presence of a potassium atom and are used for analysing the lowest unoccupied molecular orbitals participating in the collision process. From the time-of-flight mass spectra recorded in the wide collision energy range, more than 80% of the total anion yield is due to the undissociated parent anion C6Cl6-, C6Cl5- and Cl- formation. Other fragment anions such as C6Cl4-, C3Cl2-, C2Cl- and Cl2- that undergo complex internal reactions with the temporary negative ion formed after electron transfer account for less than 20% of the total yield. The joint experimental and theoretical methodologies employed in these electron transfer studies provide the most comprehensive and unique assignments of the hexachlorobenzene anionic species and the role of C6Cl6 electronic states in collision induced dissociation to date.

Spontaneous electron emission vs dissociation in internally hot silver dimer anions.

Referring to a recent experiment, we theoretically study the process of a two-channel decay of the diatomic silver anion (Ag2 -), namely, the spontaneous electron ejection giving Ag2 + e- and the dissociation leading to Ag- + Ag. The ground state potential energy curves of the silver molecules of diatomic neutral and negative ions were calculated using proper pseudo-potentials and atomic basis sets. We also estimated the non-adiabatic electronic coupling between the ground state of Ag2 - and the ground state of Ag2 + e-, which, in turn, allowed us to estimate the minimal and mean values of the electron autodetachment lifetimes. The relative energies of the rovibrational levels allow the description of the spontaneous electron emission process, while the description of the rotational dissociation is treated with the quantum dynamics method as well as time-independent methods. The results of our calculations are verified by comparison with the experimental data.

Electronic structure and rovibrational predissociation of the 21Π state in KLi.

Adiabatic potential energy curves of the 31Σ+, 33Σ+, 21Π and 23Π states correlating for large internuclear distance with the K(4s) + Li(2p) atomic asymptote were calculated. Very good agreement between the calculated and the experimental curve of the 21Π state allowed for a reliable description of the dissociation process through a small (∼20 cm-1 for J = 0) potential energy barrier. The barrier supports several rovibrational quasi-bound states and explicit time evolution of these states via the time-dependent nuclear Schrödinger equation, showed that the state populations decay exponentially in time. We were able to precisely describe the time-dependent dissociation process of several rovibrational levels and found that our calculated spectrum match very well with the assigned experimental spectrum. Moreover, our approach is able to predict the positions of previously unassigned lines, particularly in the case of their low intensity.