51
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Rasmussen AM, Ramakrishna S, Weiss EA, Seideman T. Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot. J Chem Phys 2014; 140:144102. [DOI: 10.1063/1.4870335] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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52
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Asplund E, Klüner T. A Surrogate Hamiltonian study of femtosecond photodesorption of CO from NiO(100). Mol Phys 2013. [DOI: 10.1080/00268976.2013.813589] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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53
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Füchsel G, Schimka S, Saalfrank P. On the Role of Electronic Friction for Dissociative Adsorption and Scattering of Hydrogen Molecules at a Ru(0001) Surface. J Phys Chem A 2013; 117:8761-9. [DOI: 10.1021/jp403860p] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Gernot Füchsel
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, D-14476
Potsdam-Golm, Germany
| | - Selina Schimka
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, D-14476
Potsdam-Golm, Germany
| | - Peter Saalfrank
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, D-14476
Potsdam-Golm, Germany
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54
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Mehring M, Klüner T. Calculation of two-dimensional potential energy surfaces of CO on a rutile(110) surface: ground and excited states. Mol Phys 2013. [DOI: 10.1080/00268976.2013.780106] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Matthias Mehring
- a Institut für Reine und Angewandte Chemie , Carl von Ossietzky Universität Oldenburg , Oldenburg , Germany
| | - Thorsten Klüner
- a Institut für Reine und Angewandte Chemie , Carl von Ossietzky Universität Oldenburg , Oldenburg , Germany
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55
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Pan F, Tao G. Communication: importance sampling including path correlation in semiclassical initial value representation calculations for time correlation functions. J Chem Phys 2013; 138:091101. [PMID: 23485270 DOI: 10.1063/1.4794191] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Full semiclassical (SC) initial value representation (IVR) for time correlation functions involves a double phase space average over a set of two phase points, each of which evolves along a classical path. Conventionally, the two initial phase points are sampled independently for all degrees of freedom (DOF) in the Monte Carlo procedure. Here, we present an efficient importance sampling scheme by including the path correlation between the two initial phase points for the bath DOF, which greatly improves the performance of the SC-IVR calculations for large molecular systems. Satisfactory convergence in the study of quantum coherence in vibrational relaxation has been achieved for a benchmark system-bath model with up to 21 DOF.
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Affiliation(s)
- Feng Pan
- School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen 518055, China
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56
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Füchsel G, Tremblay JC, Klamroth T, Saalfrank P. Quantum Dynamical Simulations of the Femtosecond-Laser-Induced Ultrafast Desorption of H2and D2from Ru(0001). Chemphyschem 2013; 14:1471-8. [DOI: 10.1002/cphc.201200940] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Indexed: 11/12/2022]
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57
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Petek H. Photoexcitation of adsorbates on metal surfaces: one-step or three-step. J Chem Phys 2013; 137:091704. [PMID: 22957546 DOI: 10.1063/1.4746801] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
In this essay we discuss the light-matter interactions at molecule-covered metal surfaces that initiate surface photochemistry. The hot-electron mechanism for surface photochemistry, whereby the absorption of light by a metal surface creates an electron-hole pair, and the hot electron scatters through an unoccupied resonance of adsorbate to initiate nuclear dynamics leading to photochemistry, has become widely accepted. Yet, ultrafast spectroscopic measurements of molecule-surface electronic structure and photoexcitation dynamics provide scant support for the hot electron mechanism. Instead, in most cases the adsorbate resonances are excited through photoinduced substrate-to-adsorbate charge transfer. Based on recent studies of the role of coherence in adsorbate photoexcitation, as measured by the optical phase and momentum resolved two-photon photoemission measurements, we examine critically the hot electron mechanism, and propose an alternative description based on direct charge transfer of electrons from the substrate to adsorbate. The advantage of this more quantum mechanically rigorous description is that it informs how material properties of the substrate and adsorbate, as well as their interaction, influence the frequency dependent probability of photoexcitation and ultimately how light can be used to probe and control surface femtochemistry.
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Affiliation(s)
- Hrvoje Petek
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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58
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Svensson K, Andersson S. Desorption of H2, HD, and D2 through temporary negative ion formation. PHYSICAL REVIEW LETTERS 2012; 109:196102. [PMID: 23215407 DOI: 10.1103/physrevlett.109.196102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 09/07/2012] [Indexed: 06/01/2023]
Abstract
Physically adsorbed H(2), HD, and D(2) desorbs via the low-energy 2Σ(u)+ electron scattering resonance with characteristic electron energy dependent cross sections as we show by desorption and electron energy-loss measurements. Only H(2) and HD desorb, for energetic reasons, via excitation of the j = 0 → 2 rotational mode and its subsequent decay into free translational motion, while all three isotopes desorb by direct transitions to unbound continuum states, with a probability close to unity and an unexpectedly weak mass dependence ~m(-1/2).
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Affiliation(s)
- K Svensson
- Department of Physics and Electrical Engineering, Karlstad University, SE-651 88 Karlstad, Sweden
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59
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Hyldgaard P. Nonequilibrium thermodynamics of interacting tunneling transport: variational grand potential, density functional formulation and nature of steady-state forces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:424219. [PMID: 23032101 DOI: 10.1088/0953-8984/24/42/424219] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The standard formulation of tunneling transport rests on an open-boundary modeling. There, conserving approximations to nonequilibrium Green function or quantum statistical mechanics provide consistent but computational costly approaches; alternatively, the use of density-dependent ballistic-transport calculations (e.g., Lang 1995 Phys. Rev. B 52 5335), here denoted 'DBT', provides computationally efficient (approximate) atomistic characterizations of the electron behavior but has until now lacked a formal justification. This paper presents an exact, variational nonequilibrium thermodynamic theory for fully interacting tunneling and provides a rigorous foundation for frozen-nuclei DBT calculations as a lowest-order approximation to an exact nonequilibrium thermodynamic density functional evaluation. The theory starts from the complete electron nonequilibrium quantum statistical mechanics and I identify the operator for the nonequilibrium Gibbs free energy which, generally, must be treated as an implicit solution of the fully interacting many-body dynamics. I demonstrate a minimal property of a functional for the nonequilibrium thermodynamic grand potential which thus uniquely identifies the solution as the exact nonequilibrium density matrix. I also show that the uniqueness-of-density proof from a closely related Lippmann-Schwinger collision density functional theory (Hyldgaard 2008 Phys. Rev. B 78 165109) makes it possible to express the variational nonequilibrium thermodynamic description as a single-particle formulation based on universal electron-density functionals; the full nonequilibrium single-particle formulation improves the DBT method, for example, by a more refined account of Gibbs free energy effects. I illustrate a formal evaluation of the zero-temperature thermodynamic grand potential value which I find is closely related to the variation in the scattering phase shifts and hence to Friedel density oscillations. This paper also discusses the difference between the here-presented exact thermodynamic forces and the often-used electrostatic forces. Finally the paper documents an inherent adiabatic nature of the thermodynamic forces and observes that these are suited for a nonequilibrium implementation of the Born-Oppenheimer approximation.
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Affiliation(s)
- P Hyldgaard
- Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
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60
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Menzel D. Electronically induced surface reactions: Evolution, concepts, and perspectives. J Chem Phys 2012; 137:091702. [DOI: 10.1063/1.4746799] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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61
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Bouakline F, Lüder F, Martinazzo R, Saalfrank P. Reduced and Exact Quantum Dynamics of the Vibrational Relaxation of a Molecular System Interacting with a Finite-Dimensional Bath. J Phys Chem A 2012; 116:11118-27. [DOI: 10.1021/jp304466u] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Foudhil Bouakline
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam-Golm, Germany
| | - Franziska Lüder
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam-Golm, Germany
| | - Rocco Martinazzo
- Department of Physical Chemistry and Electrochemistry, University of Milan, V. Golgi 19, 20133 Milan, Italy
| | - Peter Saalfrank
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam-Golm, Germany
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62
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Affiliation(s)
- Jan Mitschker
- Institute of Pure and Applied
Chemistry, Theoretical
Chemistry, Carl von Ossietzky Universität Oldenburg, Carl-von-Ossietzky Straße 9-11, 26129 Oldenburg, Germany
| | - Thorsten Klüner
- Institute of Pure and Applied
Chemistry, Theoretical
Chemistry, Carl von Ossietzky Universität Oldenburg, Carl-von-Ossietzky Straße 9-11, 26129 Oldenburg, Germany
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63
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Asplund E, Klüner T. Optimal control of open quantum systems: A combined surrogate Hamiltonian optimal control theory approach applied to photochemistry on surfaces. J Chem Phys 2012; 136:124118. [DOI: 10.1063/1.3698289] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
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64
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Maselli OJ, Gascooke JR, Shoji M, Buntine MA. Translational and rotational energy content of benzene molecules IR-desorbed from an in vacuo liquid surface. Phys Chem Chem Phys 2012; 14:9185-94. [DOI: 10.1039/c2cp40180k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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65
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Adsorption and photodesorption of CO from single C60 molecules studied from first principles. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.08.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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66
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67
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Mulugeta D, Watanabe K, Menzel D, Freund HJ. State-resolved investigation of the photodesorption dynamics of NO from (NO)2 on Ag nanoparticles of various sizes in comparison with Ag(111). J Chem Phys 2011; 134:164702. [DOI: 10.1063/1.3581802] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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68
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Wang LM, Sametoglu V, Winkelmann A, Zhao J, Petek H. Two-Photon Photoemission Study of the Coverage-Dependent Electronic Structure of Chemisorbed Alkali Atoms on a Ag(111) Surface. J Phys Chem A 2011; 115:9479-84. [DOI: 10.1021/jp111932r] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lei-Ming Wang
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Vahit Sametoglu
- Department of Electrical & Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada
| | - Aimo Winkelmann
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Jin Zhao
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
- Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui, China
| | - Hrvoje Petek
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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69
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Tremblay JC, Klinkusch S, Klamroth T, Saalfrank P. Dissipative many-electron dynamics of ionizing systems. J Chem Phys 2011; 134:044311. [DOI: 10.1063/1.3532410] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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70
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Füchsel G, Klamroth T, Monturet S, Saalfrank P. Dissipative dynamics within the electronic friction approach: the femtosecond laser desorption of H2/D2 from Ru(0001). Phys Chem Chem Phys 2011; 13:8659-70. [DOI: 10.1039/c0cp02086a] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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71
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Füchsel G, Klamroth T, Tremblay JC, Saalfrank P. Stochastic approach to laser-induced ultrafast dynamics: the desorption of H(2)/D(2) from Ru(0001). Phys Chem Chem Phys 2010; 12:14082-94. [PMID: 20856974 DOI: 10.1039/c0cp00895h] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The desorption of molecular hydrogen and deuterium induced by femtosecond-laser pulses is studied theoretically for the so-called DIMET (Desorption Induced by Multiple Electronic Transitions) process. These investigations are based on nonadiabatic classical Monte Carlo trajectory (CMCT) simulations on a ground and an excited state potential energy surface, including up to all six adsorbate degrees of freedom. The focus is on the hot-electron mediated energy transfer from the surface to the molecule and back, and the energy partitioning between the different degrees of freedom of the desorbing molecules. We first validate for a two-mode model comprising the desorption mode and the internal vibrational coordinate, the classical Monte Carlo trajectory method by comparing with Monte Carlo wavepacket (MCWP) calculations arising from a fully quantum mechanical open-system density matrix treatment. We then proceed by extending the CMCT calculations to include all six nuclear degrees of freedom of the desorbing molecule. This allows for a detailed comparison between theory and experiment concerning isotope effects, energy partitioning (translational, vibrational, and rotational energies and their distributions), and the dependence of these properties on the laser fluence. The most important findings are as follows. (i) CMCT agrees qualitative with the MCWP scheme. (ii) The basic experimental features such as the large isotope effect, the non-linear increase of yield with laser fluence, translationally hot products (in the order of several 1000 K) and non-equipartitioning of translational and internal energies (E(trans) > E(vib) > E(rot)) are well reproduced. (iii) Predictions concerning a strong angular dependence of translational energies at large observation angles are also made.
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Affiliation(s)
- Gernot Füchsel
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Straße 24-25, D-14476 Potsdam-Golm, Germany
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72
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Temperature effects for vibrational relaxation of hydrogen adsorbed on Si(100): a stochastic multiconfigurational time-dependent Hartree (MCTDH) study. Theor Chem Acc 2010. [DOI: 10.1007/s00214-009-0721-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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73
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Borisov AG, Sametoglu V, Winkelmann A, Kubo A, Pontius N, Zhao J, Silkin VM, Gauyacq JP, Chulkov EV, Echenique PM, Petek H. Pi resonance of chemisorbed alkali atoms on noble metals. PHYSICAL REVIEW LETTERS 2008; 101:266801. [PMID: 19113781 DOI: 10.1103/physrevlett.101.266801] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Indexed: 05/27/2023]
Abstract
We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle- and time-resolved two-photon photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known sigma resonance oriented along the surface normal, there exist long-lived alkali-localized resonances oriented parallel to the surface (pi symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.
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Affiliation(s)
- A G Borisov
- Laboratoire des Collisions Atomiques et Moléculaires, UMR CNRS-Universite Paris-Sud 8625, Bâtiment 351, Université Paris-Sud, 91405 Orsay cedex, France.
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74
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75
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Tremblay JC, Klamroth T, Saalfrank P. Time-dependent configuration-interaction calculations of laser-driven dynamics in presence of dissipation. J Chem Phys 2008; 129:084302. [DOI: 10.1063/1.2972126] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
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76
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Tremblay JC, Beyvers S, Saalfrank P. Selective excitation of coupled CO vibrations on a dissipative Cu(100) surface by shaped infrared laser pulses. J Chem Phys 2008; 128:194709. [DOI: 10.1063/1.2916710] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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77
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78
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Quasi-diabatic decoupling of Born-Oppenheimer potential energy curves for adsorbate-metal surface systems. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.03.058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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79
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Mehdaoui I, Klüner T. New mechanistic insight into electronically excited CO–NiO(100): a quantum dynamical analysis. Phys Chem Chem Phys 2008; 10:4559-64. [DOI: 10.1039/b805597a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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80
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Szymanski P, Harris AL, Camillone N. Temperature-dependent femtosecond photoinduced desorption in CO/Pd(111). J Phys Chem A 2007; 111:12524-33. [PMID: 17975899 DOI: 10.1021/jp075923w] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The desorption of CO from a Pd(111) surface following absorption of 120 fs pulses of 780 nm light occurs on two distinct and well-separated time scales. Two-pulse correlation measurements show a fast subpicosecond decay followed by a slower, approximately 40 ps decay. Simulations based on the two-temperature model of electron and phonon heat baths within the substrate, and an empirical friction model to treat coupling to the adsorbate, support the assignment of the desorption mechanism as an electron-mediated process. The photodesorption yield and overall width of the temporal response exhibit a marked dependence on the initial surface temperature in the 100-375 K range despite the much higher transient electronic temperatures (approximately 7000 K) achieved. The observed temperature dependences can be attributed directly to variations in the initial temperature within the frictional coupling picture. Simulations of this extended data set imply that the activation barrier to photoinduced desorption is equal in magnitude to that derived from thermal desorption experiments for this system within the limits of a one-dimensional Arrhenius desorption model. The simulations also imply that the slower decay is not the result of phonon-driven desorption. Though we cannot unambiguously determine the strength of the adsorbate-phonon coupling, our results suggest that its role is to moderate the degree of the adsorbate excitation.
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Affiliation(s)
- Paul Szymanski
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
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81
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Mehdaoui I, Klüner T. Bonding of CO and NO to NiO(100): a Strategy for Obtaining Accurate Adsorption Energies. J Phys Chem A 2007; 111:13233-7. [DOI: 10.1021/jp075703i] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Imed Mehdaoui
- Carl von Ossietzky Universität Oldenburg, Institut für Reine und Angewandte Chemie, Theoretische Chemie and the Center of Interface Science (CIS), Postfach 2503, D-26111 Oldenburg, Germany
| | - Thorsten Klüner
- Carl von Ossietzky Universität Oldenburg, Institut für Reine und Angewandte Chemie, Theoretische Chemie and the Center of Interface Science (CIS), Postfach 2503, D-26111 Oldenburg, Germany
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82
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Szymanski P, Harris AL, Camillone N. Adsorption-state-dependent subpicosecond photoinduced desorption dynamics. J Chem Phys 2007; 126:214709. [PMID: 17567215 DOI: 10.1063/1.2735594] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Femtosecond laser excitation has been used to initiate desorption of molecular oxygen from the (111) surface of Pd and to study the adsorption-state dependence of the substrate-adsorbate coupling. The relative populations of the two chemical states, peroxo (O2(2-)) and superoxo (O2-), were varied by changing the total coverage. Two-pulse correlation measurements exhibit a dominant 400 fs response and a slower 10 ps decay that are relatively independent of the initial O2 coverage. In contrast, the photodesorption yield and the nonlinearity of the fluence dependence show a systematic coverage dependence. The coverage-independent subpicosecond response indicates that the photoinduced desorption from the two states is driven primarily by the same electron-mediated mechanism, while the coverage dependence of the yield indicates that the desorption efficiency from the superoxo state is greater than that from the peroxo state. These results are discussed in the context of the electron-phonon two-temperature model with an empirical adsorbate-electron frictional coupling that depends on both the electronic temperature and the activation energy for desorption. With a coupling strength that decreases as the activation energy decreases, the trends with varying coverage, absorbed fluence, and time delay can all be reproduced. The model is consistent with a transition from a resonantly enhanced (diabatic) regime to an adiabatic regime as the system relaxes, accounting for the biexponential correlation behavior.
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Affiliation(s)
- Paul Szymanski
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
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83
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Abstract
The laws of thermodynamics provide a clear concept of the temperature for an equilibrium system in the continuum limit. Meanwhile, the equipartition theorem allows one to make a connection between the ensemble average of the kinetic energy and the uniform temperature. When a system or its environment is far from equilibrium, however, such an association does not necessarily apply. In small systems, the regression hypothesis may not even apply. Herein, it is shown that in small nonequilibrium systems, the regression hypothesis still holds, though with a generalized definition of the temperature. The latter must now be defined for each such manifestation.
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Affiliation(s)
- Alexander V Popov
- Center for Computational and Molecular Science and Technology, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
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