Transcript Chemistry and Spectroscopy with Free Electrons

Measuring and modeling absolute data
for electron-induced processes
Chemistry and Spectroscopy with Free Electrons
A personal retrospective
Michael Allan
Department of Chemistry
University of Fribourg, Switzerland
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Contents
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
2
Pardubice
Electron Tubes
gloooooooow in the dark
magic eye
3
Basel
Energy of incident electron
Energy of emitted photon
M. Allan and J. P. Maier 1976
4
Yale
M. J. W. Boness and G. J. Schulz 1976
A. Stamatovic and G. J. Schulz 1970
5
short – lived radical anions = resonances
q = 72°
background
scattering
coherent
superposition
resonant
scattering
6
E
(eV)
DEA and VE in H2
Resonances:
Feshbach (sg)13s2
valence core-excited (sg)1(su)2
shape (sg)2(su)1
“s* shape resonance”
Ethreshold
H-/H2
> 200
D-/D2
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Frustration over instruments
• Background
• Low energy not accessible
• Only narrow energy range
• Spectrum distorted by instrument’s response
function
• Only relative units
• Limited angular range
•
...
M. J. W. Boness and G. J. Schulz 1973 8
Fribourg
1981
1989
• Very low background
• Low energy OK
• Wide energy range
• but
• Only relative units
• scattering angle only 0° and 180°
• no elastic scattering
9
Magnetic Angle Changer
Magnetic Angle Changer
(Frank H. Read)
see also Andrew J. Murray, Wednesday lecture
10
Time-of-Flight mass spectrometer
for absolute DEA cross section
Juraj Fedor, Olivier May, Dušan Kubala, Fribourg 2008
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12
13
full-range spectrum in N2
core excited Feshbach resonance
shape resonances
14
H2 : a short or long-lived resonance?
15
H2 : a short or long-lived resonance?
E
(eV)
1985
calculations:
Čížek, Horáček, Domcke
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1993
looking at large R (high
final v) permits time
resolution
17
H2- lifetime : going to the extreme
D2 : t = 2 ms
Experiment : Golser et al., 2005 (Wienna)
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Threshold phenomena
Vibrational excitation in HF – naive expectation
s* - resonance
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Threshold phenomena
• threshold peaks
• Vibrational Feshbach Resonances
s* shape resonance
• dipole – bound resonances
valence
dipole - bound
m = 1.8 D
Čížek, Horáček, Allan, Fabrikant, Domcke 2003
Original discovery: G. Knoth, M. Gote, M. Rädle, K. Jung and H. Ehrhardt, PRL 1989
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HF – theory and experiment
Čížek, Horáček, Allan, Fabrikant, Domcke, J. Phys. B (2003)
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 excitation
boomerang 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)
23
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 theory
red: absolute experiment
dissociative attachment
cross section drops when
a new vibrational
excitation channel opens
Fedor May Allan (2008)
Čížek Horáček Sergenton Popović Allan
Domcke Leininger Gadea
Phys. Rev. A 63 (2000) 062710
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to remember:
long range (dipole) attraction

„nonlocal phenomena“
Vibrational Feshbach Resonances
threshold peaks in VE
large 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
27
Exciting the Fermi-dyad in CO2
virtual state
p* shape resonance
Allan, Phys. Rev. Lett. 87 (2001)
Excitation of the Fermi – split
states is highly selective!
28
Cross section for exciting the topmost member of
the tetrad {(3000), (2200), ... }
Allan, (2011, in print)
29
Similarity of vibrational cross sections in CO2 and HF
m=0D
m = 1.8 D
30
Potential curves of CO2 and HF
bending
Physica Scripta (2004)
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Allan, J. Phys. B (2002)
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Understanding the selectivity within the dyad
FIG. 3. Contour plots of the wave functions for the two
components 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
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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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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
theory:
S. T. Chourou and A. E. Orel 2009
experiment:
O. May, J. Fedor, B. C. Ibanescu and M. Allan 2009
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Dissociative Electron Attachment to Acetylene
S. T. Chourou and A. E. Orel PRA 2008
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Dissociative Electron Attachment to Acetylene
S. 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
ring breathing
C-Cl stretch
- the p* resonances act as doorway states into the s* resonance
- no activation barrier ← symmetry lowering ← vibronic coupling
Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002
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Two families of DEA:
HBr
H-C≡C-H
• no shape resonance
• p* shape resonance
• peak at threshold
• peak at resonance
• steps
• LCP sufficient
• nonlocal theory required
• inherently multidimensional
O
H
Puzzle: mechanism in formic acid ?
C
O
H
• both p* shape resonance and polar O-H bond
HCOOH + e-  HCOO- + H
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Vibrational excitation of formic acid
41
Vibrational excitation of formic acid
- cusps, like HCl, HBr, HF
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HCOOH + e-  HCOO- + H : approach I
theory: R-matrix
G. A. Gallup, P. D. Burrow and
I. I. Fabrikant PRA 2009
experiment
A. Pelc, W. Seiler, P. Scheier, N.
J. Mason, E. Illenberger and T.
Märk 2003 & 2005
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approach II
O
H
neutral
C
O
p* anion
s* anion
H
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Dissociation of formic acid anion
on the valence p* shape resonance potential surface
Isotope effect expected for D substitution on C-H
DFT B3-LYP 6-31G*
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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
50
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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Rydberg states: potential curves
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TD-DFT, pbe0/6-311++g(3df,3p), geometry: DFT b3lyp/6-311+g(2df,2p)
Bogdan Ibanescu 2007
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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Ne
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
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Some research groups active
in electron collisions
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Sanche and co-workers:
slow electrons damage DNA
Martin, Burrow, Cai, Hunting,
Sanche, Phys. Rev. Lett. 2004
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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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
Gdansk
•
Mariusz Zubek, Marcin Dampc
•
cross sections, magnetic angle changer
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
Belgrad
•
Bratislav Marinkovic, Aleksandar Milosavljević, Zoran Petrovic
•
cross sections
Orsay
•
Robert Abouaf, Roger Azria, Ann Lafosse
•
cross sections, surfaces
Roma
•
Franco Gianturco, Isabella Baccarelli
•
theory
Bremen
•
Petra Swiderek
•
electron collisions with molecules in cold matrices
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London
•
JonathanTennyson
•
R-matrix theory
Aarhus
•
David Field, Oksana Plekan
•
very low energies, ferroelectricity
Island
•
Oddur Ingólfsson
•
experiment, DEA
Tata Institute, Mumbai
•
E. Krishnakumar, S. V. K. Kumar, V. Prabhudesai
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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
Korea
•
Hyuck Cho
•
magnetic angle changer, cross sections
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Tokyo
•
Hiroshi Tanaka
•
cross sections
Drake University
•
Klaus Bartschat, Oleg Zatsariny
•
theory
Caltech
•
Vince McKoy, Carl Winstead
•
theory
Fullerton, CA
•
Morty Khakoo
•
cross sections
Australia
•
Stephen Buckman, Michael Brunger, ...
•
transient molecules, metastable atoms, positrons
Australia
•
Igor Bray, Dmitry Fursa, Laurence Campbell
•
theory
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Where do we find
electron – driven chemistry and physics?
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Electron – Driven Chemistry: gas phase
- 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
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ROBUST SCIENCE,
SOCIETAL BENEFIT
· 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.
Ref: Adapted from “Plasma Science:
Advancing Knowledge in the
National Interest”, US National
Research Council, 2007.
GEC2010
slide by Prof. Mark J. Kushner
University of Michigan
68
Institute for Plasma Science & Engr.
with permission
Resonance in Hg
Angle-integrated cross section for electron-impact excitation of
the (6s6p) 3P0o state of mercury from the (6s2) 1S0 ground state.
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SUCCESS AT CONTROLLING
f(e): 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.html
http://antwrp.gsfc.nasa.gov/apod/ap970830.html
http://www.eere.energy.gov/buildings/info/documents/
pdfs/lmc_vol1_final.pdf
GEC2010
· Optimizing f(e) in plasma lighting by 0.1
eV translates into three 1-GWe plants.
· This is an incredible accomplishment and
mastery of discharge physics.
slide by Prof. Mark J. Kushner
University of Michigan
Institute for Plasma Science & Engr.
with permission
70
Conclusions
validate theory by
comparing absolute
(differential) cross
sections for :
- elastic scattering
- vibrational
- electronic
- DEA
c.f. photochemistry
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Electron-driven physics and chemistry
Where are we ?
theory
threshold phenomena
DEA:
diatomics OK
multidimensional
phenomena
H-C≡C-H ; LCP only
polyatomics ?
elastic scattering
vibrational excitation
Feshbach/shape reson.
Rydberg/valence
conical intersections
H2O, CO2 ; only beginning
electronic excitation
experiment
-
full set of absolute cross sections measured for only few molecules
DEA : angular distributions
transient molecules (CF2 , metastables)
surfaces, liquids
- Much remains to be done
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Wolfgang Domcke
Rainer Dressler
Jiří Horáček
Louis Neuhaus
Martin Čížek
Bruno Albrecht
Karel Houfek
Knut Asmis
Roman Čurik
Christophe Bulliard
Petr Čársky
Olivier Schafer
Jean-Pierre Gauyacq
Anne-Christelle Sergenton
Arvid Herzenberg
Duška Popović
Ilya I Fabrikant
Momir Stepanović
Tom Rescigno
Tomáš Skalický
Ann Orel
Svetlana Živanov
Bill McCurdy
Bogdan Ibanescu
Klaus Bartschat
Olivier May
Juraj Fedor
Dušan Kubala
Emil Brosi
Paul-Hervé Chassot
Lorenz Cederbaum
Gleb Gribakin
Olivier Graber
Hartmut Hotop
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Spin-orbit components of the NO ground electronic term
Allan, Phys. Rev. Lett. (2004)
75
sideline : Associative Electron Detachment
dissociative electron attachment (DEA)
e–(E) + HBr  H + Br–
and the reverse process
associative electron detachment (AED)
Br– + H  HBr( ,J) + e–(E)
related by the microscopic reversibility, but AD probes much higher J
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sideline : Associative Electron Detachment
- 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 !
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associative electron detachment
Interchannel coupling in associative
detachment dramatically influences
product state distribution
Živanov, Allan, Čížek, Horáček, Thiel, Hotop, Phys. Rev. Lett. (2002)
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