A number of dynamical processes involving hydrogen atoms on graphite surfaces is addressed by means of time-dependent quantum dynamical calculations. These processes are relevant for hydrogen formation in interstellar clouds, where molecular formation has been long hypothesized to occur on the surface of dust grains. Firstly, hydrogen formation via Eley- Rideal recombination is studied within the rigid, flat surface approximation [1] starting from both chemisorbed and physisorbed species, with some emphasis on unexpected quantum effects in the reaction dynamics at high collision energies [2]. Competitive processes such as collision induced desorption of adsorbed species and adsorbate-induced trapping are also discussed. Secondly, the special behavior of the dynamics in the so-called cold collision energy regime (i.e. for collision energies down to 1 K) is considered with a zero-energy twowavepackets approach. Thirdly, tunneling diffusion of physisorbed hydrogen atoms at T=0 K is modeled with wavepacket dynamics on a new ab-initio Potential Energy Surface based on correlated wavefunction calculations on a cluster model [3]. Extension of the model to chemisorption is also discussed with the aim of assessing the reliability of available Density- Functional-Theory data. Fourthly, our work in progress in dealing with energy dissipation to the surface is presented. Specifically, the Local Coherent-State Approximation (LCSA) to system-bath quantum dynamics [4] is introduced and results of model calculations are presented and compared to the exact Multi Configuration Time-Dependent Hartree ones. These model calculations comprise vibrational relaxation, tunneling dynamics and surface sticking in systems with 50-80 bath (surface) degrees of freedom. Extensions to realistic problems and T>0 K dynamics are discussed, with some emphasis on the good (linear) scaling properties of the LCSA method with respect to the bath size. References 1. M. Persson and B. Jackson, J. Chem. Phys., 102, 1078 (1995); D. Lemoine and B. Jackson, Comp. Phys. Comm. 137, 415 (2001) 2. R. Martinazzo and G. F. Tantardini, J. Phys. Chem. A, 109, 9379 (2005); J. Chem. Phys. 124, 124702 (2006); 124, 124703 (2006) 3. M. Bonfanti, R. Martinazzo, G. F. Tantardini and A. Ponti, J. Phys. Chem. C, 111, 5825 (2007) 4. R. Martinazzo, M. Nest, P. Saalfrank and G. F. Tantardini, J. Chem. Phys., 125, 194102 (2006).

Quantum studies of Hydrogen dynamics on graphite surfaces / R. Martinazzo. ((Intervento presentato al convegno Elementary Reactive Processes at Surfaces tenutosi a Donostia, Spain nel 2007.

Quantum studies of Hydrogen dynamics on graphite surfaces

R. Martinazzo
Primo
2007

Abstract

A number of dynamical processes involving hydrogen atoms on graphite surfaces is addressed by means of time-dependent quantum dynamical calculations. These processes are relevant for hydrogen formation in interstellar clouds, where molecular formation has been long hypothesized to occur on the surface of dust grains. Firstly, hydrogen formation via Eley- Rideal recombination is studied within the rigid, flat surface approximation [1] starting from both chemisorbed and physisorbed species, with some emphasis on unexpected quantum effects in the reaction dynamics at high collision energies [2]. Competitive processes such as collision induced desorption of adsorbed species and adsorbate-induced trapping are also discussed. Secondly, the special behavior of the dynamics in the so-called cold collision energy regime (i.e. for collision energies down to 1 K) is considered with a zero-energy twowavepackets approach. Thirdly, tunneling diffusion of physisorbed hydrogen atoms at T=0 K is modeled with wavepacket dynamics on a new ab-initio Potential Energy Surface based on correlated wavefunction calculations on a cluster model [3]. Extension of the model to chemisorption is also discussed with the aim of assessing the reliability of available Density- Functional-Theory data. Fourthly, our work in progress in dealing with energy dissipation to the surface is presented. Specifically, the Local Coherent-State Approximation (LCSA) to system-bath quantum dynamics [4] is introduced and results of model calculations are presented and compared to the exact Multi Configuration Time-Dependent Hartree ones. These model calculations comprise vibrational relaxation, tunneling dynamics and surface sticking in systems with 50-80 bath (surface) degrees of freedom. Extensions to realistic problems and T>0 K dynamics are discussed, with some emphasis on the good (linear) scaling properties of the LCSA method with respect to the bath size. References 1. M. Persson and B. Jackson, J. Chem. Phys., 102, 1078 (1995); D. Lemoine and B. Jackson, Comp. Phys. Comm. 137, 415 (2001) 2. R. Martinazzo and G. F. Tantardini, J. Phys. Chem. A, 109, 9379 (2005); J. Chem. Phys. 124, 124702 (2006); 124, 124703 (2006) 3. M. Bonfanti, R. Martinazzo, G. F. Tantardini and A. Ponti, J. Phys. Chem. C, 111, 5825 (2007) 4. R. Martinazzo, M. Nest, P. Saalfrank and G. F. Tantardini, J. Chem. Phys., 125, 194102 (2006).
Settore CHIM/02 - Chimica Fisica
Quantum studies of Hydrogen dynamics on graphite surfaces / R. Martinazzo. ((Intervento presentato al convegno Elementary Reactive Processes at Surfaces tenutosi a Donostia, Spain nel 2007.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/185215
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