Chemical Dynamics Theory Group

In the field of the interstellar chemical processes, we are studying two ionic systems, the LiH₂⁺ and the CH₂⁺ systems. The first is the most important one in the Lithium ionic network of the Primordial Universe and it is interesting for the destructive reactions of LiH⁺ and LiH:

LiH⁺ + H → Li⁺ + H + H

LiH + H⁺ → Li + H₂⁺

accurate analytical potential has been fitted to 11000 MRVB energies, already available, and to 600 MRCI energies calculated with "chemically accurate" a basis set. This potential is being used to obtain, within a classical and a quantum mechanical approach, the rate constants for the above LiH⁺/LiH reactions, in an astrochemically interesting range of temperatures.

The CH₂⁺ system is the "node" of Carbon Chemistry in recent interstellar clouds where it could help to solve the 'CH⁺mystery'.

We are computing very accurate MRCI potential energy surfaces for the three lowest electronic states, i.e., those involved in the Renner-Teller interaction (which charact1erizes the equilibrium geometry of the ground state), and in the conical intersection (which might influence the radiative formation of CH₂⁺ from C⁺ and H₂).

This research will continue with a classical calculation of the rate constants ("Surface Hopping" approach), and then with an exact quantum mechanical treatment.

In the field of surface processes, we are studying the Hydrogen recombination process on the (100) surface of Nickel. This system can be considered a prototype for the study of "direct" recombination reactions of light atoms on catalyzing surfaces. In particular, we are investigating the Eley-Rideal and the Hot–Atom reaction mechanisms.

We used both the rigid surface model and the more realistic moving surface model, in which energy exchange between the incoming H atom and the H-covered surface is allowed. Particular attention has been devoted to the characterization of the Hot–Atoms (average life time, formation cross sections, etc.), which could play a decisive role when the surface is covered by adsorbates. Next goal will be the study of the dynamics when several H atoms are adsorbed on the surface, and of the role of the substrate geometry on the reaction kinetics.

A Time Dependent quantum mechanical treatment of the H atoms dynamics is also being considered.

Our interest in studies of electronic structure of metallic thin films prompted us to perform DFT–GGA calculations on a Pb(111) film, 1 to 15 layers thick.

Total energy and electronic density have been computed using plane waves and ultrasoft pseudopotentials, in the slab–supercell approach. Their oscillations with the number of layers have been related to Quantum Size Effects, as observed experimentally in the epitaxial growth of Pb films on a Cu(111) substrate, using the Helium scattering technique.

To improve the treatment, we will compute a potential energy surface for the He-surface interaction, and then we will perform dynamical simulations in which the Time Dependent Wave Packet approach will be used to describe the He atom motion, whereas the motion of the metal atoms will be treated classically.

We are interested in the formation of a bilayer of H₂O molecules on the Ru(0001). Despite the plethora of experiments, many are the problems still open.

We performed a series of DFT–GGA calculations on the Ru(0001) surface, naked and H₂O covered, using plane waves and ultrasoft pseudopotentials, in the slab-supercell approach.

From fully relaxed calculations, we have obtained information on geometry and energetics of the adsorption, both for intact and half–dissociated bilayers.

Comparison of the geometric parameters with the available experimental data shows that, in agreement with Feibelman, only the half–dissociated structure is able to reproduce the bilayer buckling, but a detailed analysis of the electronic structure properties rises some doubt on the actual origin of water dissociation in the famous Held-Menzel LEED–IV experiment.