Electron scattering cross sections from anthracene over a broad energy range (0.00001-10,000 eV)

We report a computational investigation of electron scattering by anthracene (C14H10) in the gas phase. Integral and differential cross sections have been calculated by employing two distinct ab-initio quantum scattering methods: the symmetry adapted-single centre expansion method (ePOLYSCAT) and a screening corrected form of the independent atom model (IAM-SCAR) at low and high energies, respectively. After a detailed evaluation of the current results, we present a complete set of integral scattering cross sections from 0.00001 to 10,000 eV.

Modeling chemical evolution in a cold molecular plasma: quantum dynamics of CF2(-) intermediates after electron attachment

A dynamical study is presented for the chemical processes induced by electrons (with energies up to about 16 eV) on gaseous CF(2) (X(1)A(1) state), one of the important components of plasma etching molecular mixtures. The nuclear deformations from the C(2v) initial geometry are seen to lead to different anionic intermediates that suggest different chemical evolutions into final fragments. All nuclear motions are shown to be effective for the formation of a variety of resonances which could lead to different final fragments. The effect of the above vibrational activation of the transient anionic states initially formed at the equilibrium geometry is analyzed and discussed in detail, providing compelling evidence and physical reasons for the fragment observations given by various experiments on such plasmas.

Ring-breaking electron attachment to uracil: following bond dissociations via evolving resonances

Calculations are carried out at various distinct energies to obtain both elastic cross sections and S-matrix resonance indicators (poles) from a quantum treatment of the electron scattering from gas-phase uracil. The low-energy region confirms the presence of pi(*) resonances as revealed by earlier calculations and experiments which are compared with the present findings. They turn out to be little affected by bond deformation, while the transient negative ions (TNIs) associated with sigma(*) resonances in the higher energy region ( approximately 8 eV) indeed show that ring deformations which allow vibrational redistribution of the excess electron energy into the molecular target strongly affect these shape resonances: They therefore evolve along different dissociative pathways and stabilize different fragment anions. The calculations further show that the occurrence of conical intersections between sigma(*) and pi(*)-type potential energy surfaces (real parts) is a very likely mechanism responsible for energy transfers between different TNIs. The excess electron wavefunctions for such scattering states, once mapped over the molecular space, provide nanoscopic reasons for the selective breaking of different bonds in the ring region.

Replacement equivalence of H- and argon in small (Ar)nH- clusters from optimized structure calculations

The structural properties of some of the smaller ionic clusters of argon atoms containing the atomic impurity H-, ArnH- with n from 2 up to 7, are examined using different modeling for the interactions within each cluster and by employing different theoretical treatments, both classical and quantum, for the energetics. The same calculations are also carried out for the corresponding neutral homogeneous clusters Ar(n+1). The results of the calculations, the physical reliability of the interactions modeling, and the similarities and the difference between the anionic and the neutral complexes are discussed in some detail. The emerging picture shows that, due to specific features of the employed atom-atom potentials, the ArnH- and Ar(n+1) clusters present very similar structures, where the H- dopant substitutes for one of the outer Ar atoms but does not undergo as yet solvation within such small clusters.

Ab initio quantum dynamics with very weak van der Waals interactions: Structure and stability of small Li2(1Sigmag+)-(He)n clusters

The potential energy surface (PES) for the interaction between Li2(1Sigmag+) and 4He has been computed using an accurate, post-Hartree-Fock quantum calculation for its ground electronic state. The orientational anisotropy of the forces and the interplay between repulsive and attractive effects within the PES are analyzed to extract information on the possible existence of bound states in the triatomic system. The structures of a few of the Li2(He)n small clusters are examined by comparing a classical approach with a full quantum one to generate bound configurations and to extract information on the possible spatial arrangements of the smaller clusters via à vis the location of the Li2 dopant. Some significant consequences on the Li2 behavior in larger clusters and droplets are drawn from the above findings.

Rotational quenching in ionic systems at ultracold temperatures

The behavior of the rotational quenching for a molecular ion in collision with closed-shell neutral gases is investigated. We confirm that Wigner's threshold law for inelastic scattering holds in the presence of a long-range interaction due to polarization forces decreasing as the inverse fourth power of the distance but find that, because of the contributions of the higher angular momenta, its range of applicability is markedly reduced when compared to the scattering by neutral species. The calculations of the quenching cross sections make evident the special features of ionic systems at ultralow collision energies and yield rate coefficients of the order of 10(-9) x cm(3) x s(-1), much larger than those found for the quenching of neutral molecules.