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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

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dynamics of spin triplet and spin singlet o 2 on clean ag 100 surfaces

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)
slide2

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

slide3

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

slide4

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

slide5

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)

slide6

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

slide7

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).

slide8

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)
slide9

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)]

slide10

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

slide11

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

slide12

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

slide13

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
slide14

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

slide15

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

slide16

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

slide17

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

slide18

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

slide19

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

slide20

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!)

slide21

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

slide22

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.
slide24

M. Alducin

H. F. Busnengo

R. Díez Muiño

Dynamics of spin-triplet and spin-singlet O2

on clean Ag(100) surfaces

slide25

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

why o 2 on ag 100
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).

dissociative dynamics of o 2 ag 100 classical trajectory calculations
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

dissociative dynamics of o 2 ag 100 classical trajectory calculations1
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

dissociative dynamics of o 2 ag 100 classical trajectory calculations2
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

dissociative dynamics of o 2 ag 100 classical trajectory calculations3
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

reactivity of spin singlet o 2 on the ag 100 surface
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

dissociative dynamics of spin singlet o 2 on ag 100
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
dissociative dynamics of spin singlet o 2 on ag 1001
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
dynamics of spin triplet versus spin singlet o 2
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

dynamics of spin triplet versus spin singlet o 22
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

thank you for your attention
Thank you for your attention !

Gas/solid interfaces Group

(San Sebastián)

CFM

Centro de Física de Materiales

Donostia International Physics Center

work in progress and open questions
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

dynamics on nsp pes1
Dynamics on NSP PES

Note: (Different scales in Y-axis)

technical details ab initio sp pes
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

thank you for your attention1
Thank you for your attention !

CFM

Centro de Física de Materiales,

Centro Mixto CSIC-UPV/EHU