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
1
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
7
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
11
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
16
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)
18
Threshold phenomena
Vibrational excitation in HF – naive expectation
s* - resonance
19
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
20
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.
21
structures everywhere
22
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
-
24
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
25
to remember:
long range (dipole) attraction

„nonlocal phenomena“
Vibrational Feshbach Resonances
threshold peaks in VE
large CS and steps in DEA
26
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)
31
Allan, J. Phys. B (2002)
32
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
33
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
34
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
35
Dissociative Electron Attachment to Acetylene
S. T. Chourou and A. E. Orel PRA 2008
36
Dissociative Electron Attachment to Acetylene
S. T. Chourou and A. E. Orel
37
Chlorobenzene
Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002
38
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
39
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
40
Vibrational excitation of formic acid
41
Vibrational excitation of formic acid
- cusps, like HCl, HBr, HF
42
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
43
approach II
O
H
neutral
C
O
p* anion
s* anion
H
44
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*
45
Isotope effect
D. Kubala, O. May, M. Allan, 2011
46
Formic acid is a prototype for biomolecules :
forms hydrogen bonds !
M Allan, Phys. Rev. Lett. (2007)
47
Similar situation in other biomolecules : uracil
48
Family III: higher energies
On the complexity of dissociation via core-excited Feshbach resonances
in polyatomic molecules
49
Feshbach resonances
50
photoelectron spectra are
useful in predicting
Feshbach resonances
Bogdan Ibanescu 2007
51
O-C bond does
not dissociate !
Bogdan Ibanescu 2007
52
Rydberg states: potential curves
53
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)
54
Pt(PF3)4 : vibrational states
55
Pt(PF3)4 : fragmentation
O. May, D. Kubala, poster Mo 038
56
Atoms
great success of theory !
57
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
58
Some research groups active
in electron collisions
59
Sanche and co-workers:
slow electrons damage DNA
Martin, Burrow, Cai, Hunting,
Sanche, Phys. Rev. Lett. 2004
Science, 2004
60
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
61
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
62
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
63
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
•
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
64
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
65
Where do we find
electron – driven chemistry and physics?
66
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
67
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.
69
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
71
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
72
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
73
74
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
76
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 !
77
associative electron detachment
Interchannel coupling in associative
detachment dramatically influences
product state distribution
Živanov, Allan, Čížek, Horáček, Thiel, Hotop, Phys. Rev. Lett. (2002)
78