Making and Breaking of Chemical Bonds: Dynamics of elementary reactions from gas phase to condensed phase

The present thesis is concerned with the dynamics of elementary chemical reactions. In particular, the processes of bond formation (association) and of bond cleavage (dissociation) are studied. Both photo-induced and solvent-induced reaction mechanisms are elucidated. By embedding simple diatomic model systems in rare gas clusters and matrices, the transition of the dynamics of making and breaking of chemical bonds from the gas phase to the condensed phase is systematically investigated

The He + H2+ → HeH+ + H reaction: Ab initio studies of the potential energy surface, benchmark time-independent quantum dynamics in an extended energy range and comparison with experiments

The following article appeared in Journal of Chemical Physics 137.24 (2012): 244306 and may be found at http://scitation.aip.org/content/aip/journal/jcp/137/24/10.1063/1.4772651In this work we critically revise several aspects of previous ab initio quantum chemistry studies [P. Palmieri, Mol. Phys. 98, 1835 (2000); C. N. Ramachandran, et al., Chem. Phys. Lett. 469, 26 (2009)] of the HeH2+ system. New diatomic curves for the H2+ and HeH+ molecular ions, which provide vibrational frequencies at a near spectroscopic level of accuracy, have been generated to test the quality of the diatomic terms employed in the previous analytical fittings. The reliability of the global potential energy surfaces has also been tested performing benchmark quantum scattering calculations within the time-independent approach in an extended interval of energies. In particular, the total integral cross sections have been calculated in the total collision energy range 0.955-2.400 eV for the scattering of the He atom by the ortho- and para-hydrogen molecular ion. The energy profiles of the total integral cross sections for selected vibro-rotational states of H2+ (v = 0,...,5 and j = 1,... ,7) show a strong rotational enhancement for the lower vibrational states which becomes weaker as the vibrational quantum number increases. Comparison with several available experimental data is presented and discussedThe work has been performed under the HPC-EUROPA2 project (Project No.: 228398) with the support of the European Commission - Capacities Area - Research Infrastructures. D.D.F., V.A., and S.C. thank also the Italian MIUR for PRIN contracts. A.A. acknowledges support by the program CONSOLIDERINGENIO of Ministerio de Economia y Competitividad (Spain) under Grant No. CSD2009-00038, entitled “Molecular Astrophysics: the Herschel and Alma Era,” Grant No. FIS2011-29596-C02-02, and by Comunidad Autonoma de Madrid (CAM) under Grant No. S-2009/MAT/146

General Mathematical Formulation of Scattering Processes in Atom-Diatomic Collisions in the RmatReact Methodology

Accurately modelling cold and ultracold reactive collisions occuring over deep potential wells, such as \ce{D+ + H2 -> H+ + HD}, requires the development of new theoretical and computational methodologies. One potentially useful framework is the R-matrix method adopted widely for electron-molecule collisions which has more recently been applied to non-reactive heavy particle collisions such as Ar-Ar. The existing treatment of non-reactive elastic and inelastic scattering needs to be substantially extended to enable modelling of reactive collisions: this is the subject of this paper. Herein, we develop the general mathematical formulation for non-reactive elastic and inelastic scattering, photo-association, photo-dissociation, charge exchange and reactive scattering using the R-matrix method. Of particular note is that the inner region, of central importance to calculable R-matrix methodologies, must be finite in all scattering coordinates rather than a single scattering coordinate as for non-reactive scattering. % The choice of coordinate set and basis function is these cases becomes more complexThis introduces substantial challenges to the basis sets utilised in practical calculations as integrals over finite domains are often much more challenging than over infinite domains for this problem.Comment: Submitted as part of the issue of Phil. Trans. Roy. Soc. A special issue on "Advances in hydrogen molecular ions: H3+, H5+ and beyond

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N2, O2, NO), Mars (CO2, CO, N2) and Jupiter (H2, He) atmospheres are considered

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N-2, O-2, NO), Mars (CO2, CO, N-2) and Jupiter (H-2, He) atmospheres are considered