measuring and modeling absolute data for electron-induced processes

1

Measuring and modeling absolute data for electron-induced processes

Michael Allan

Department of Chemistry

University of Fribourg, Switzerland

Chemistry and Spectroscopy with Free Electrons

A personal retrospective

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1. A very personal retrospective

2. H2 : a short or long-lived resonance?

3. The peculiar story of threshold peaks : HF, HCl, HBr

4. CO2 : threshold peaks are commonplace

5. H-C≡C-H : the necessity of many dimensions

6. HCOOH : the hybrid case

7. Higher energy : CH3OH, C4H9-O-C4H9 etc.

8. Exotic molecules: Pt(PF3)4

9. Many excellent laboratories

10. Where do we find electron collisions ?

11. Conclusions

Contents

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gloooooooow in the dark

Electron Tubes

magic eye

Pardubice

4

Basel

M. Allan and J. P. Maier 1976

Energy of emitted photon

Energy of incident electron

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Yale

M. J. W. Boness and G. J. Schulz 1976 A. Stamatovic and G. J. Schulz 1970

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short – lived radical anions = resonances

backgroundscattering

resonantscattering

coherent

superposition

= 72°

7

Feshbach (g)13s2

valence core-excited (g)1(u)2

Resonances:

shape (g)2(u)1

DEA and VE in H2

“* shape resonance”

Ethreshold

H-/H2

D-/D2

> 200

E(eV)

8

Frustration over instruments

M. J. W. Boness and G. J. Schulz 1973

• Background

• Low energy not accessible

• Only narrow energy range

• Spectrum distorted by instrument’s response function

• Only relative units

• Limited angular range

• ...

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Fribourg

• Very low background

• Low energy OK

• Wide energy range

• but

• Only relative units

• scattering angle only 0° and 180°

• no elastic scattering

1981 1989

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Magnetic Angle Changer(Frank H. Read)

Magnetic Angle Changer

see also Andrew J. Murray, Wednesday lecture

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Juraj Fedor, Olivier May, Dušan Kubala, Fribourg 2008

Time-of-Flight mass spectrometer

for absolute DEA cross section

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13

14shape resonances

core excited Feshbach resonance

full-range spectrum in N2

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H2 : a short or long-lived resonance?

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E(eV)

H2 : a short or long-lived resonance?

1985

calculations:Čížek, Horáček, Domcke

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looking at large R (high final v) permits time resolution

1993

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H2 lifetime : going to the extreme

D2 : = 2 ms

Experiment : Golser et al., 2005 (Wienna)

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Vibrational excitation in HF – naive expectation

* - resonance

Threshold phenomena

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• threshold peaks

• Vibrational Feshbach Resonances

• dipole – bound resonances

* shape resonance

valence

dipole bound

Čížek, Horáček, Allan, Fabrikant, Domcke 2003

= D

Threshold phenomena

Original discovery: G. Knoth, M. Gote, M. Rädle, K. Jung and H. Ehrhardt, PRL 1989

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Čížek, Horáček, Allan, Fabrikant, Domcke, J. Phys. B (2003)

HF – theory and experiment

review: Hotop, Ruf, Allan, Fabrikant, Adv. At. Mol. Opt. Phys. 49 (2003) pp 85-216.

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structures everywhere

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NO – vibrational excitationboomerang oscillations strongly influenced by existence of

quasi-bound vibrational state of NO

Allan, J. Phys. B (2005)

K. Houfek, M. Čížek, J. Horáček, Chem. Phys. (2008)

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Chemistry:

Dissociative electron attachment to

diatomic hydrides

e + HBr H + Br

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Interchannel Coupling in Dissociative Atachment

COMPARISON OF ABSOLUTE CROSS SECTIONS !

blue: nonlocal resonance theoryred: absolute experiment

Fedor May Allan (2008)

Čížek Horáček Sergenton Popović Allan Domcke Leininger GadeaPhys. Rev. A 63 (2000) 062710

dissociative attachment cross section drops when a new vibrational excitation channel opens

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to remember:

long range (dipole) attraction „nonlocal phenomena“

Vibrational Feshbach Resonancesthreshold peaks in VElarge CS and steps in DEA

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CO2

has no dipole moment – is it like H2 ?

Fermi Resonance

the (1000) and (0200) vibrations mix

true states: {(1000) + (0200)}

(Fermi dyad) {(1000) - (0200)}

two Raman lines

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Excitation of the Fermi – split states is highly selective!

Allan, Phys. Rev. Lett. 87 (2001)

virtual state * shape resonance

Exciting the Fermi-dyad in CO2

29Allan, (2011, in print)

Cross section for exciting the topmost member of the tetrad {(3000), (2200), ... }

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Similarity of vibrational cross sections in CO2 and HF

D D

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Potential curves of CO2 and HF

Physica Scripta (2004)

bending

32Allan, J. Phys. B (2002)

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FIG. 3. Contour plots of the wave functions for the twocomponents of the Fermi dyad in O-C-O angle. The thick line marks the seam where the anion and neutral surfaces cross. Top panel: upper member of dyad; bottom panel: lower member of dyad.

Vanroose et al. PRL 2004

Understanding the selectivity within the dyad

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Until now: effects due to long range electron binding: • threshold peaks in VE• sharp structures in VE cross sections• Vibrational Feshbach resonances• large cross sections and threshold peaks in DEA• steps in DEA cross section• theory: nonlocal theory essential• existing theory: one dimension (diatomic or pseudodiatomic)

Next: effects due several dimensions of nuclear motion:

• symmetry-lowering due to vibronic coupling

• anion needs to distort in order to dissociate

• theory: several dimensions of nuclear motion essential

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theory:S. T. Chourou and A. E. Orel 2009

experiment:O. May, J. Fedor, B. C. Ibanescu and M. Allan 2009

isotope ratio:

experiment : 14.4

theory at 0 K : 28.9

theory at 333 K : 17.9

but :

theoretical cross section nearly 2× too large

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Dissociative Electron Attachment to AcetyleneS. T. Chourou and A. E. Orel PRA 2008

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Dissociative Electron Attachment to AcetyleneS. T. Chourou and A. E. Orel

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Chlorobenzene

Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002

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Chlorobenzene

- the * resonances act as doorway states into the * resonance

- no activation barrier ← symmetry lowering ← vibronic coupling

Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002

ring breathing C-Cl stretch

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Two families of DEA:

Puzzle: mechanism in formic acid ? • both * shape resonance and polar O-H bond

HBr• no shape resonance

• peak at threshold

• steps

• nonlocal theory required

H-C≡C-H• * shape resonance

• peak at resonance

• LCP sufficient

• inherently multidimensional

C

O

O

H

H

HCOOH + e HCOO + H

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Vibrational excitation of formic acid

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Vibrational excitation of formic acid

- cusps, like HCl, HBr, HF

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HCOOH + e HCOO + H : approach I

theory: R-matrixG. A. Gallup, P. D. Burrow and I. I. Fabrikant PRA 2009

experimentA. Pelc, W. Seiler, P. Scheier, N. J. Mason, E. Illenberger and T. Märk 2003 & 2005

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* anion * anionneutralC

O

O

H

H

approach II

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Dissociation of formic acid anionon the valence * shape resonance potential surface

DFT B3-LYP 6-31G*

Isotope effect expected for D substitution on C-H

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Isotope effect

D. Kubala, O. May, M. Allan, 2011

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Formic acid is a prototype for biomolecules : forms hydrogen bonds !

M Allan, Phys. Rev. Lett. (2007)

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Similar situation in other biomolecules : uracil

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Family III: higher energies

On the complexity of dissociation via core-excited Feshbach resonances

in polyatomic molecules

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Feshbach resonances

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photoelectron spectra are useful in predicting Feshbach resonances

Bogdan Ibanescu 2007

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O-C bond does not dissociate !

Bogdan Ibanescu 2007

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Bogdan Ibanescu 2007TD-DFT, pbe0/6-311++g(3df,3p), geometry: DFT b3lyp/6-311+g(2df,2p)

Rydberg states: potential curves

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a recent example : Pt(PF3)4

(a FEBIP precursor)

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Pt(PF3)4 : vibrational states

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Pt(PF3)4 : fragmentation

O. May, D. Kubala, poster Mo 038

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Atoms

great success of theory !

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Absolute cross sections for excitation of the Ne (2p53s) states at θ = 180°.

M Allan, K Franz, H Hotop, O Zatsarinny and K Bartschat 2008

Ne

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Some research groups

active in electron

collisions

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Martin, Burrow, Cai, Hunting, Sanche, Phys. Rev. Lett. 2004

Sanche and co-workers:slow electrons damage DNA

Science, 2004

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Sherbrooke, Canada

• Léon Sanche

• biomolecules, surfaces, theory

Lincoln, Nebraska

• Paul Burrow, Gordon Gallup, Ilya Fabrikant

• DEA, theory

Davis & Berkeley, CA

• Ann Orel, Tom Rescigno, Bill McCurdy : theory

• H. Adaniya : DEA experiment - COLTRIMS

Belfast

• Tom Field; Gleb Gribakin

• ToF DEA, biomolecules; theory

Kaiserslautern

• Hartmut Hotop

• ultrahigh resolution, ultralow energy

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Gdansk

• Mariusz Zubek, Marcin Dampc

• cross sections, magnetic angle changer

Innsbruck

• Paul Scheier, Tilmann Märk, Stefan Denifl

• biomolecules, electron collisions in He nanodroplets

Berlin

• Eugen Illenberger

• DEA, biomolecules

Open University, Milton Keynes

• Nigel Mason, Jimena Gorfinkiel

• European leadership, theory

Bratislava, Slovakia

• Stefan Matejcik

• DEA

University of Podlasie, Poland

• Janina Kopyra

• DEA, electron transport

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Prague, Charles University

• Jiří Horáček, Martin Čížek, Karel Houfek (+ Wolfgang Domcke)

• theory

Prague Heyrovský Institute

• Petr Čársky, Roman Čurik

• theory

Orsay

• Robert Abouaf, Roger Azria, Ann Lafosse

• cross sections, surfaces

Belgrad

• Bratislav Marinkovic, Aleksandar Milosavljević, Zoran Petrovic

• cross sections

Roma

• Franco Gianturco, Isabella Baccarelli

• theory

Bremen

• Petra Swiderek

• electron collisions with molecules in cold matrices

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Tata Institute, Mumbai

• E. Krishnakumar, S. V. K. Kumar, V. Prabhudesai

• DEA experiment : velocity slice imaging

Brazil

• Marco Lima, M.H.F. Bettega, Romarly F. da Costa, M.-T. Lee and Ione Iga

• theory, high energy experiment

Island

• Oddur Ingólfsson

• experiment, DEA

Korea

• Hyuck Cho

• magnetic angle changer, cross sections

Aarhus

• David Field, Oksana Plekan

• very low energies, ferroelectricity

London

• JonathanTennyson

• R-matrix theory

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Drake University

• Klaus Bartschat, Oleg Zatsariny

• theory

Caltech

• Vince McKoy, Carl Winstead

• theory

Fullerton, CA

• Morty Khakoo

• cross sections

Australia

• Igor Bray, Dmitry Fursa, Laurence Campbell

• theory

Australia

• Stephen Buckman, Michael Brunger, ...

• transient molecules, metastable atoms, positrons

Tokyo

• Hiroshi Tanaka

• cross sections

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Where do we find

electron – driven chemistry and physics?

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- Outer space

- Ionosphere: northern light etc.

- Industrial plasmas- semiconductor manufacture- flat displays

- plasma displays- LCD display manufacture- back-lighting: Xe excimer

- surface modification- hydrophilic- hydrophobic- shrink-proof wool- milk packaging- …

- waste disposal- satellite engines

Electron – Driven Chemistry: gas phase

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· Low Temperature Plasma Science and Technology has a history and future of robust, interdisciplinary science challenges whose resolution provides immediate and long term societal benefit.

ROBUST SCIENCE,SOCIETAL BENEFIT

slide by Prof. Mark J. KushnerUniversity of Michigan

Institute for Plasma Science & Engr.with permissionGEC2010

Ref: Adapted from “Plasma Science: Advancing Knowledge in the National Interest”, US National Research Council, 2007.

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Angle-integrated cross section for electron-impact excitation of the (6s6p) 3P0

o state of mercury from the (6s2) 1S0 ground state.

Resonance in Hg

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SUCCESS AT CONTROLLING f(): PLASMA LIGHTING

· Annual US electrical power consumption: 3.5 x 1012 kW-Hr

· Electrical power expended in lighting: 22% - in fluorescent lamps: 9%

· 35 1-GWe power plants are used to excite a single multiplet of Hg in fluorescent lamps.http://www.eia.doe.gov/cneaf/electricity/epa/epates.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970830.html http://www.eere.energy.gov/buildings/info/documents/ pdfs/lmc_vol1_final.pdf

· Optimizing f() in plasma lighting by 0.1 eV translates into three 1-GWe plants.

· This is an incredible accomplishment and mastery of discharge physics.

GEC2010

slide by Prof. Mark J. Kushner

University of MichiganInstitute for Plasma Science & Engr.

with permission

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validate theory by comparing absolute (differential) cross sections for :- elastic scattering- vibrational- electronic- DEA

Conclusions

c.f. photochemistry

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Where are we ?

- Much remains to be done

Electron-driven physics and chemistry

theory

DEA: threshold phenomena

diatomics OK

polyatomics ?

multidimensional phenomena

H-C≡C-H ; LCP only

Feshbach/shape reson.Rydberg/valence conical intersectionsH2O, CO2 ; only beginning

elastic scattering vibrational excitation electronic excitation

experiment - full set of absolute cross sections measured for only few molecules

- DEA : angular distributions

- transient molecules (CF2 , metastables)

- surfaces, liquids

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Rainer Dressler

Louis Neuhaus

Bruno Albrecht

Knut Asmis

Christophe Bulliard

Olivier Schafer

Anne-Christelle Sergenton

Duška Popović

Momir Stepanović

Emil Brosi

Paul-Hervé Chassot

Olivier Graber

Tomáš Skalický

Svetlana Živanov

Bogdan Ibanescu

Olivier May

Juraj Fedor

Dušan Kubala

Wolfgang Domcke

Jiří Horáček

Martin Čížek

Karel Houfek

Roman Čurik

Petr Čársky

Jean-Pierre Gauyacq

Arvid Herzenberg

Ilya I Fabrikant

Tom Rescigno

Ann Orel

Bill McCurdy

Klaus Bartschat

Lorenz Cederbaum

Gleb Gribakin

Hartmut Hotop

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Spin-orbit components of the NO ground electronic term

Allan, Phys. Rev. Lett. (2004)

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Br– + H HBr( ,J) + e–(E)

e–(E) + HBr H + Br–

dissociative electron attachment (DEA)

associative electron detachment (AED)

related by the microscopic reversibility, but AD probes much higher J

and the reverse process

sideline : Associative Electron Detachment

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- Collision parameter b determines J

- energy of departing electron carries information about final , J

- this permits recording cross section as a function of J for each !

sideline : Associative Electron Detachment

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Interchannel coupling in associative detachment dramatically influences product state distribution

Živanov, Allan, Čížek, Horáček, Thiel, Hotop, Phys. Rev. Lett. (2002)

associative electron detachment