A theoretical investigation on the spectrum of the Ar trimer for high rotational excitations.

A detailed study of the rovibrational spectrum of the Ar trimer is performed by means of an exact hyperspherical coordinate (HC) method and a variational approach based on distributed Gaussian functions (DGFs) to describe the interparticle distances. The good agreement observed between the energy levels obtained with both procedures for high values of the total angular momentum (J=15 and 20) reveals the quality of the DGF method to describe the rotation of the title system. Rotational constants for the lowest bound states, obtained as averages for each vibrational state, have been obtained and compared to previous results. A detailed analysis of density probability functions obtained by means of the HC approach for rovibrational states at J=0 and 20 shows close similitudes thus supporting the vibration-rotation separation adopted within the DGF scheme for the Ar(3) system.

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.

Competitive bond breaking in floppy molecular trimers: HeNeH and HeNeH- calculations.

Calculations for the J=0 bound states associated with the two title molecular systems are carried out using distributed Gaussian function approach and using the sum of two-body potential approximation to describe the overall interactions. The results yield one bound state for the neutral trimer and three bound states for the anionic triatom. The relative values of dissociation energies place the first dissociation threshold at the H emission for the neutral complex and at the He emission for the corresponding anion. The general spatial properties of the various bound states are analyzed on both systems.

Electron-attachment resonances of glycine zwitterions from quantum scattering calculations: modeling macrosolvation effects.

A computational study of the quantum dynamics for low-energy electrons scattered by the isolated zwitterionic species of the glycine molecule is carried out using a model interaction potential described in the main text. The macroscopic effects of water solvation on the target molecule in the electron scattering problem are described through a continuum polarizable model (CPCM) which modifies the target molecular structure. In such a way, realistic molecular orbitals depicting the glycine zwitterion in solution are used to model the electron-molecule interaction. The results of the calculations indicate the presence of five different transient negative ions (TNIs) formed at energies from the threshold and up to about 6 eV. Although no nuclear motion was explicitly considered in the ensuing decay processes, the analysis of the nodal structures and density distributions for the resonant excess electron wavefunctions over the molecular space suggests possible anionic fragmentations that produce (Gly-H)-, H-, -CO2-, and -NH3. The likely consequences of such releases into the medium are briefly discussed.

A complete configurational study for the bound states of Ne trimers.

The structural properties and the energetics of the ground and the excited bound states of Ne(3) for zero total angular momentum are examined using different modelings for the two-body interactions. We employ a method consisting of a variational approach with a distributed Gaussian functions (DGF) basis set expansion. We discuss at length the advantages and possible limitations of such an approach, comparing it to other methods which have been applied in the literature to the same system. The DGF method turns out to be very accurate in giving us the bound states energetics and also provides in a natural way a convincing pictorial description of all the states, including those with dominant linear configurations. Additional bound states are found for the Ne(3) system with respect to those indicated in previous works and we suggest a "stabilization" procedure that can be used to assess the truly bound nature of a state. Some considerations on the relative reliability of the examined two-body interactions are also reported.

Bound-state energies in argon trimers via a variational expansion: the effects from many-body corrections.

In this paper we study the bound-state energies and geometries of Ar(3) for J=0, using the distributed Gaussian functions method that provides a configurational description of the different structures contributing to these states. Atom-atom potentials are employed and three-body long-range effects are also included in the computational treatment by adding to the sum of potentials the Axilrod-Teller triple-dipole correction for the whole rotationless energy spectrum. An estimate of the total number of bound states for the Ar trimer is given. With respect to previous calculations, limited to the lower-lying states, our results show slightly larger nonadditive effects and are further able to predict the full range of the bound spectrum. Changes on the geometries of a large part of the vibrationally excited states of Ar(3) when the Axilrod-Teller term is included in the molecular potential are found by the present study.

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.