arXiv subjects

E. Bodo

Publications and source records attributed to E. Bodo.

6 recordsLinked to original sources

arXiv2007

Collisional Quenching at Ultralow Energies: Controlling Efficiency with Internal State Selection

Calculations have been carried out for the vibrational quenching of excited H$_2$ molecules which collide with Li$^+$ ions at ultralow energies. The dynamics has been treated exactly using the well known quantum coupled-channel expansions over different initial vibrational levels. The overall interaction potential has been obtained from the calculations carried out earlier in our group using highly correlated ab initio methods. The results indicate that specific features of the scattering observables, e.g. the appearance of Ramsauer-Townsend minima in elastic channel cross sections and the marked increase of the cooling rates from specific initial states, can be linked to potential properties at vanishing energies (sign and size of scattering lengths) and to the presence of either virtual states or bound states. The suggestion is made that by selecting the initial state preparation of the molecular partners, the ionic interactions would be amenable to controlling quenching efficiency at ultralow energies.

physics.chem-ph↗

arXiv2007

Low energy H+CO scattering revisited: CO rotational excitation with new potential surfaces

A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0->1 rotational transition. New close-coupling (CC) rigid-rotor calculations for CO(v=0,J=0) excitation by H are performed on four different PESs. Two of the PESs are obtained in this work using state-of-the-art quantum chemistry techniques at the CCSD(T) and MRCI levels of theory. Cross sections for the J=0->1, as well as other odd Delta J, transitions are significantly suppressed compared to even Delta J transitions in thermal energy CC calculations using the CCSD(T) and MRCI surfaces. This is consistent with a expected even Delta J propensity and in contrast to CC calculations using the earlier WKS PES which predict a dominating 0->1 transition. The current results suggest that the original astrophysical assumption that excitation of CO by H_2 dominates the kinetics of CO in diffuse ISM gas is likely to remain valid.

astro-ph↗

arXiv2007

Microsolvation of cationic dimers in $^4$He droplets: geometries of A$_2^+$(He)$_N$ (A=Li,Na,K) from optimized energies

Ab initio computed interaction forces are employed in order to describe the microsolvation of the A$_2^+(^2Σ)$ (A=Li,Na,K) molecular ion in $^4$He clusters of small variable size. The minimum energy structures are obtained by performing energy minimization based on a genetic algorithm approach. The symmetry features of the collocation of solvent adatoms around the dimeric cation are analyzed in detail, showing that the selective growth of small clusters around the two sides of the ion during the solvation process is a feature common to all three dopants.

physics.chem-ph↗

arXiv2007

Bosonic Helium droplets with cationic impurities: onset of electrostriction and snowball effects from quantum calculations

Variational MonteCarlo and Diffusion MonteCarlo calculations have been carried out for cations like Li$^+$, Na$^+$ and K$^+$ as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms. The interaction has been modelled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab-initio calculations over a broad range of interatomic distances. This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are here discussed in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the clusters features.

physics.chem-ph↗

arXiv2005

Microsolvation of Li$^+$ in small He Clusters. Li$^+$He$_n$ species from Classical and Quantum Calculations

A structural study of the smaller Li$^+$He$_n$ clusters with $n\le30$ has been carried out using different theoretical methods. The structures and the energetics of the clusters have been obtained using both classical energy minimization methods and quantum Diffusion Monte Carlo. The total interaction acting within the clusters has been obtained as a sum of pairwise potentials: Li$^+$-He and He-He. This approximation had been shown in our earlier study \cite{8} to give substantially correct results for energies and geometries once compared to full ab-initio calculations. The general features of the spatial structures, and their energetics, are discussed in details for the clusters up to $n=30$ and the first solvation shell is shown to be essentially completed by the first ten helium atoms.

physics.chem-ph↗

arXiv2005

Neutral and ionic dopants in helium clusters: interaction forces for the $Li_2(a^3Σ_u^+)-He$ and $Li_2^+(X^2Σ_g^+)-He$

The potential energy surface (PES) describing the interactions between $\mathrm{Li_{2}(^{1}Σ_{u}^{+})}$ and $\mathrm{^{4}He}$ and an extensive study of the energies and structures of a set of small clusters, $\mathrm{Li_{2}(He)_{n}}$, have been presented by us in a previous series of publications [1-3]. In the present work we want to extend the same analysis to the case of the excited $\mathrm{Li_{2}}(a^{3}Σ_{u}^{+})$ and of the ionized Li$_{2}^{+}(X^{2}Σ_{g}^{+})$ moiety. We thus show here calculated interaction potentials for the two title systems and the corresponding fitting of the computed points. For both surfaces the MP4 method with cc-pV5Z basis sets has been used to generate an extensive range of radial/angular coordinates of the two dimensional PES's which describe rigid rotor molecular dopants interacting with one He partner.

physics.chem-ph↗