1 / 46

Dynamics of spin-triplet and spin-singlet O 2 on clean Ag(100) surfaces

Dynamics of spin-triplet and spin-singlet O 2 on clean Ag(100) surfaces. Maite Alducin Ricardo Díez Muiño Centro de Física de Materiales CSIC-UPV/EHU Donostia-San Sebastián ( Spain ). H. Fabio Busnengo Instituto de Física Rosario IFIR CONICET – UNR Rosario (Argentina). M. Alducin

garrison-jennings
Download Presentation

Dynamics of spin-triplet and spin-singlet O 2 on clean Ag(100) surfaces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dynamics of spin-triplet and spin-singlet O2on clean Ag(100) surfaces Maite Alducin Ricardo Díez Muiño Centro de Física de Materiales CSIC-UPV/EHU Donostia-San Sebastián (Spain) H. Fabio Busnengo • Instituto de Física Rosario IFIR • CONICET – UNR • Rosario (Argentina)

  2. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces motivation desorption dissociative adsorption molecular adsorption staticproperties (equilibrium) dynamical properties • - adsorption sites and energies • chemical bonding • induced reconstructions • self-assembling • reaction rates • (adsorption, recombination, …) • - diffusion • - induced desorption • - energy and charge exchange experimental techniques: - LEED, STM, PE, etc. experimental techniques: - molecular beams, TPD, etc. an important goal is to understand how solid surfaces can be used to promote gas-phase chemical reactions

  3. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces motivation desorption dissociative adsorption molecular adsorption dissociative adsorption Q Ei staticproperties (equilibrium) dynamical properties  • - adsorption sites and energies • chemical bonding • induced reconstructions • self-assembling • reaction rates • (adsorption, recombination, …) • - diffusion • - induced desorption • - energy and charge exchange • adsorption probability depends on: • incidence kinetic energy • initial rovibrational state • incidence angle experimental techniques: - LEED, STM, PE, etc. experimental techniques: - molecular beams, TPD, etc. an important goal is to understand how solid surfaces can be used to promote gas-phase chemical reactions

  4. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces adiabatic approximation We assume that the time-dependent potential is changing so slowly that the electronic wave function rearranges to the new ground state at any instant of time: The system remains in its instantaneous eigenstate. Surface excited electronic states are not relevant

  5. M. Alducin H. F. Busnengo R. Díez Muiño Exposure (ML) Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces electronic excitations experimental evidence vibrationalpromotion of electron transfer chemicurrents Gergen et al., Science 294, 2521 (2001). Huang et al., Science 290, 111 (2000) White et al., Nature 433, 503 (2005) role of electronic friction Surface electronic excitations at the surface can be considered as decoupled polar angle of incidence Qi=0 Trail et al., JCP 119, 4539 (2003) Luntz et al., JCP 123, 074704 (2005) Díaz et al., PRL 96, 096102 (2006) Nieto et al., Science 312, 86 (2006). sticking coefficient Qi=45 Juaristi et al., PRL 100, 116102 (2008) Luntz et al., PRL 102, 109601 (2009) (comment) Juaristi et al., PRL 102, 109602 (2009) (reply) Qi=60 initial kinetic energy (eV)

  6. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces O2 on metal surfaces non-adiabatic effects in the incoming O2 molecule Yourdshahyan et al., PRB 65, 075416 (2002) Behler et al., PRL 94, 036104 (2005) Carbogno et al. PRL 101, 096104 (2008) Yourdshahyan et al., PRB 65, 075416 (2002) Behler et al., PRL 94, 036104 (2005) Carbogno et al. PRL 101, 096104 (2008) Surface electronic excitations are created in the system

  7. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces O2 /Ag Q Ei molecular beamexperimentson flat Ag surfaces • Ts < 150K: O2 adsorbs only molecularly (Ei< 1eV)  • Ag (111) • Ag (100)/Ag(110) Lowprobability • dissociation of O2 on Ag(100) • possible ways to enhance dissociation: • role of excited electronic states? 70% A. Raukema et al., Surf. Sci. 347, 151 (1996). L. Vattuone et al., Surf. Sci. 408, L698 (1998).

  8. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces O2/Ag(100) - theoretical calculations Q Ei calculation of thePotentialEnergySurface (PES) z • Born-Oppenheimer approximation • frozen surface approximation  6D PES: V(X, Y, Z, r, q, j) q Z  r Y y X j classical trajectorycalculations surfaceunitcell x • incidence conditions are fixed: • (Ei, Q) • Monte-Carlo samplingonthe • internaldegrees of freadom: • (X, Y, q, j) and on  (parallel velocity)

  9. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces building the 6D PES numerical procedure DFT energy data • O2 in vacuum spin-triplet ground state: • DFT - GGA (PW91) calculation with VASP • plane-wave basis set and US pseudopotentials • periodic supercell: (2 x 2) and 5-layer slab y hollow top view front view x top bridge z • about 2300 spin-polarized DFT values • interpolation of the DFT data: Corrugation reducing procedure [Busnengo et al., JCP 112, 7641 (2000)]

  10. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces relevant configurations Dissociativeconfiguration Molecular potentialwell • Energy depth: • Ewell~ -0.25 eV • Position: • Over hollow • θ=90o • Z≈1.6 Å • r ≈ 1.4 Å • Energy barrier: • E~ 1.1 eV • Position: • Over bridge • θ=90º • Z≈1.5 Å Ag(100) surfaceunitcell Ag(100) surfaceunitcell

  11. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation probability Q=0o

  12. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation probability Q=30o Q=0o

  13. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation probability Q=30o Q=0o Q=45o • General features: • Activation energy: ~1.1eV • Low dissociation probability Q=60o 2D Potentialenergysurface Reason: Only configurations around bridge lead to dissociation • Energy barrier: • E~ 1.1 eV • Position: • Z≈1.5 Å

  14. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces the question can we enhance O2 dissociation on clean Ag(100) ? Gas phase O2 6D PES calculation: Non spin polarized DFT 1Dg 1 eV singlettotriplet excitationenergy 3Sg

  15. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces differences between SP and NSP PESs z q Z r Gas phase O2 Y 1Dg Non spin polarized y X j 1 eV singlettotriplet excitationenergy surfaceunitcell x Spin polarized 3Sg for Z < 2A, the SP and NSP PESs merge

  16. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation is enhanced for singlet O2 Q=0o Q=30o Q=45o spin-triplet O2 spin-triplet O2 spin-triplet O2 spin-singlet O2 spin-singlet O2 spin-singlet O2 dissociation occursforEi < 1 eV dissociation can increase in oneorder of magnitude

  17. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation is enhanced for singlet O2 Q=0o Q=30o Q=45o But there is a trick here! The total energy is 1 eV larger for the singlet O2 spin-triplet O2 spin-triplet O2 spin-triplet O2 spin-singlet O2 spin-singlet O2 spin-singlet O2 Gas phase O2 1Dg 1 eV singlettotriplet excitationenergy 3Sg dissociation occursforEi < 1 eV dissociation can increase in oneorder of magnitude

  18. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces dissociation is enhanced for singlet O2 Q=0o Q=30o Q=45o spin-triplet O2 spin-triplet O2 spin-triplet O2 spin-singlet O2 spin-singlet O2 spin-singlet O2 1 eV 1 eV 1 eV dissociation occursforEi < 1 eV dissociation can increase in oneorder of magnitude for Q ≠ 0o, singlet-O2 is more efficient than triplet-O2 with the same total energy

  19. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces why is that? spin-triplet O2 spin-singlet O2 1 eV 1 eV

  20. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces why is that? spin-triplet O2 spin-singlet O2 available paths to dissociation are different (and more!)

  21. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces it is not the same road singlet O2 triplet O2 triplet O2 singlet O2 + 1 eV

  22. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces conclusions • The low dissociation of O2 on Ag(100) is due to two main factors: • - The existence of large activation energy barriers of about 1eV. • - Only a small number of configurations in phase space lead to • dissociation. • Dissociation increases in about one order of magnitud, if singlet–O2 • molecular beams are used. • Under off-normal incidence angles, the efficiency of singlet-O2 to • dissociation is remarkable: it exceeds the reactivity of triplet-O2 • with an extra kinetic energy of 1eV.

  23. thank you for your attention

  24. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces

  25. M. Alducin H. F. Busnengo R. Díez Muiño Dynamics of spin-triplet and spin-singlet O2 on clean Ag(100) surfaces it is not the same road singlet O2 triplet O2 + 1 eV singlet O2 triplet O2

  26. Why O2on Ag(100) ? Q Ei Molecular beamexperimentson flat Ag surfaces • Ts < 150K: O2 adsorbs only molecularly (Ei< 1eV, )  • Ag (111) • Ag (100)/Ag(110) Lowprobability • Dissociation of O2 on Ag(100) • reasons for the lack of dissociation • possible ways to enhance dissociation: • role of excited electronic states? 70% A. Raukema et al., Surf. Sci. 347, 151 (1996). L. Vattuone et al., Surf. Sci. 408, L698 (1998).

  27. Dissociative dynamics of O2/Ag(100): Classical trajectory calculations Ei=1.5 eV Q=0o Z=3.5 Å 3.5 Å Ag(100) unitcell

  28. Dissociative dynamics of O2/Ag(100): Classical trajectory calculations Ei=1.5 eV Q=0o Z=3.5 Å 3.5 Å 2.0 Å Z=2 Å Ag(100) unitcell

  29. Dissociative dynamics of O2/Ag(100): Classical trajectory calculations Ei=1.5 eV Q=0o Z=3.5 Å 3.5 Å 2.0 Å 1.5 Å Z=2 Å Z=1.5 Å Ag(100) unitcell

  30. Dissociative dynamics of O2/Ag(100): Classical trajectory calculations Ei=1.5 eV Q=0o Ei=2 eV Q=0o Z=3.5 Å 3.5 Å 2.0 Å 1.5 Å Z=2 Å Z=1.5 Å Ag(100) unitcell Ag(100) unitcell

  31. Reactivity of spin-singlet O2on the Ag(100) surface • PES calculation: Non spin polarized DFT • Z < 2A: SP and NSP PESs merging Gas phase O2 • Classicaltrajectorycalculations 1Dg Non spin polarized NSP PES 1 eV singlettotriplet excitationenergy Surface Spin polarized 3Sg SP PES

  32. Dissociativedynamics of spin-singlet O2 on Ag(100) Q=0o Q=30o Q=45o spin-triplet O2 spin-triplet O2 spin-triplet O2 spin-singlet O2 spin-singlet O2 spin-singlet O2 • DissociationoccursforEi < 1 eV • Dissociation can increase in oneorder of magnitud

  33. Dissociativedynamics of spin-singlet O2 on Ag(100) Q=0o Q=30o Q=45o spin-triplet O2 spin-triplet O2 spin-triplet O2 spin-singlet O2 spin-singlet O2 spin-singlet O2 1 eV 1 eV 1 eV • DissociationoccursforEi < 1 eV • Dissociation can increase in oneorder of magnitud • ForQ ≠ 0o, singlet-O2is more efficientthan triplet-O2withhigherEi

  34. Dynamics of spin-triplet versus spin-singlet O2 spin-triplet O2 spin-singlet O2 num.rebounds >3 num.rebounds <3 direct Surface trapping Dissociationis a directprocess Dynamictrappingalsoimportant

  35. Dynamics of spin-triplet versus spin-singlet O2 1 eV 1 eV

  36. Dynamics of spin-triplet versus spin-singlet O2 1 eV 1 eV Under off-normal incidence angles, the efficiency of singlet-O2 to dissociation is due to the existence of more paths leading to dissociation

  37. Thank you for your attention ! Gas/solid interfaces Group (San Sebastián) CFM Centro de Física de Materiales Donostia International Physics Center

  38. Work in progress and open questions Molecular trapping vs Molecular sticking Molecular potentialwell No energybarriers in theentrancechannel !! • Energy depth: • Ewell~ -0.25 eV • Position: • Over hollow • θ=90o • Z≈1.6 Å • r ≈ 1.4 Å Experimental data from L. Vattuone et al., Surf. Sci. 408, L698 (1998) Ag(100) surfaceunitcell

  39. Dynamics on NSP PES

  40. Dynamics on NSP PES Note: (Different scales in Y-axis)

  41. NSP vs ‘adiabatic’ singlet O2 Qi=0

  42. Direct vs indirect in ‘adiabatic singlet-PES’

  43. NSP PES: RPBE vs PW91

  44. Technical details: Ab initio SP PES Dependence of the difference between NSP and SP energies on the distance from the surface Z Filled symbols: DFT values Open symbols: Interpolated values

  45. Thank you for your attention ! CFM Centro de Física de Materiales, Centro Mixto CSIC-UPV/EHU

More Related