DISSOCIATIVE ELECTRON ATTACHMENT IN MOLECULES - NEEDS AND CURRENT STATUS OF AVAILABLE DATA

1
DISSOCIATIVE ELECTRON ATTACHMENT IN MOLECULES -
NEEDS AND CURRENT STATUS OF AVAILABLE DATA

• Iztok Cadež
• Jožef Štefan Institute, Jamova cesta 39, 1000
  Ljubljana, Slovenia
• E-mail iztok.cadez_at_ijs.si

Regional workshop on atomic and molecular data,
Belgrade, Serbia, June 14-16, 2012
2
Outline

• DISSOCIATIVE ELECTRON ATTACHMENT IN MOLECULES -
  NEEDS AND CURRENT STATUS OF AVAILABLE DATA
• - Introduction
• - Historic overview
• - DEA in some details (TCS, PCS, I(?),)
• - Applications and needs
• - Available data
• - Perspectives

3
Introduction

• Many types of elementary collision processes for
  numerous atomic particles are needed to be well
  known for the variety of collective phenomena to
  be understood.
• Here we will present only fragmentary, personal
  view on one of such processes, dissociative
  electron attachment, which is one channel of one
  kind (resonant) of one pair of collision partners
  (electron neutral molecule).

4
Introduction

• e AB ? AB- ? A B-
• A, B atoms or atomic groups
• a resonant process specific peaked energy
  dependence, typ. lt 15 eV(!)
• alternative compound state decay by
  autodetachment resonant electron scattering)
• symmetry selection rules angular distribution
  of dissociating fragment
• energy partition among kinetic and internal
  degrees of freedom
• temperature dependence DEA to excited target.

5
Introduction

• e AB ? AB- ? A B-

Anzai et al., Cross section data sets for
electron collisions with H2, O2, CO, CO2, N2O and
H2O, Eur. Phys. J. D (2012) 66 36
6
Historic overview

• First experimental evidence of DEA

J. T. Tate and P. T. Smith, Phys. Rev. (1932) 39
270
7
Historic overview

• In late fifties a strong interest for DEA started
• Early the most active centers for DEA research
• Bell Telephone Labs. H. D. Hagstrum (1951)
• Westinghouse Labs. G. J. Schulz, P. J. Chantry
  (1959-1968)
• USSR V. I. Khvostenko, V. M. Dukelskii, I. S.
  Buchelnikova (1957-)
• Liverpool University J. D. Craggs (1959)
• NBS/JILA (G. Dunn 1962)
• Lockheed Missiles and Space Comp. D. Rapp et
  al. (1965)
• Yale University - G. J. Schulz, and his group
  (1967-1981)
• University Orsay, Paris F. Fiquet-Fayard (1972)
• First theoretical approaches borrowed from
  nuclear science (J. N. Bardsley, A. Herzenberg,
  T. F. OMalley, H. S. Taylor, Yu. N. Demkov)
  (1962-).

8
Historic overview

• The study of atomic collisions in Belgrade
  started after the return of Milan Kurepa from
  postgraduate visit in the laboratory of professor
  J. D. Craggs at the University of Liverpool in
  1963. Soon after this, Vladeta Uroševic (electron
  impact photo-excitation and swarms, IFB) and
  Branka Cobic (heavy- particle collisions, Vinca)
  entered actively in the field.

Milan Kurepa (1933-2000)
Soon also started very active theoretical work
initiated by Ratko Janev (Vinca) after his return
from Ph.D. stay in Lenjingrad (StPetersburg) and
Petar Grujic after his return from Ph.D. stay at
UC, London.
Good seed good soil good weather
conditions (environment) good timing (goals)
dedicated work plenty of good results!
9
Historic overview

• Later development of DEA research included
  detailed partial CS determination from triatomic
  and some bigger molecules, study of angular
  distribution of product anions and temperature
  dependence of DEA CS.
• After somehow lower intensity of this research in
  eighties and nineties new boom occurred in more
  recent time by development of COLTRIMS concept
  and position sensitive detection and driven by
  new areas of interest.
• Theory has been steadily developing and following
  new experimental findings.

10
Present time key experimental tool - VMI
Historic overview
Adaniya et al., Rev. Sci. Instrum. (2012) 83
023106
Nandi et al., Rev. Sci. Instrum. (2005) 76 053107
Wu et al., Rev. Sci. Instrum. (2012) 83 013108
11
Present key experimental tool - VMI
Historic overview
Adaniya et al., Rev. Sci. Instrum. (2012) 83
023106
12
Total cross section measurements

• Experimental studies were initially concentrated
  on the relative and absolute cross section
  measurements for total anion production.

Cadež, Pejcev and Kurepa, J. Phys. D Appl.
Phys. (1983) 16 305
Tate-Smith type apparatus for TCS, incorporating
TEM was constructed in Belgrade in early
seventies. Studied molecules were O2, CO2,
CCl2F2, BF3, Cl2, Br2, SO2 and some more.
Christophorou et al., 1984.
13
Total cross section measurements - H2 case
This case spans over almost entire period of
modern time DEA studies!
e H2(v) ? H2- ? H H -
H2
D2
Isotope effect is common in DEA as atomic mass
determines the speed of dissociation and
therefore brunching to this channel of resonant
decay. This is the most pronounced for H vs. D
100 of mass difference!
E. Krishnakumar, S. Danifl, I. Cadež, S. Markelj
and N. J. Mason, PRL 106 (2011) 243201
14
Partial cross section measurements

• Coupling with fragment ion mass analysis allowed
  determination of partial cross section for
  production of particular negative ion.

From Matejcík et al. Int. J. Mass Spec. (2003)
223-224 9
Such arrangements are/were used at Yale,
Innsbruck, Bratislava, Berlin, Belgrade...
Braun et al., Int. J. Mass Spec. (2006) 252
234 Inter laboratory cooperation on specific
target is very important and fruitful!
15
Angular distribution of fragment anion

• For diatomics very clear interpretation as AD is
  a mirror image of attachment probability fast
  dissociation along molecular axis (O2, NO, CO,
  H2).

From Van Brunt and Kieffer, Phys. Rev. A
(1970) 2 1293 1899
16
Angular distribution of fragment anion
Charm of the experimental studies of atomic
collisions is permanent development of elegant
and more or less simple technical improvements!
Modifying standard electron spectrometer by
incorporating simple momentum filter for
elimination of electrons allowed high resolution
ion energy and angular measurements!

• O-/CO Cadež et al., J.Phys.B. (1975), 8 L73
  Hall et al., Phys. Rev. A (1978), 15 599
  Schermann et al., J.Phys.E., (1978) 11 746

17
Angular distribution of fragment anion

• H-/H2O Haxton et al., 2006 (theory) Adaniya et
  al., 2012 (experiment)

• For small polyatomics interpretation more
  difficult due to complicated few body motion
  consequently, much less studied (H2O, H2S).
• For big biomolecules, interpretation is again
  easier due to large mass of neutral fragment
  remains to be studied and it has very high
  importance for dense media.

18
Energy partition

• Measurement of fragment ion energy allows
  determination of the excited state in which
  neutral fragment is left.

e AB ? AB- ? A B-
Ee Ei-ex Ef-ex Ek D - EA EKB- MA/MAB
EK
Most atoms and many radicals have positive EA.
H- from H2O Belic et al., J.Phys.B (1981) 14 175
Hall et al., Phys. Rev. A (1978) 15 599
19
DEA to excited target
Electron collisions with excited targets are
frequent in hot media an overview in L. C.
Christophorou and J. K. Olthoff, Electron
interactions with excited atoms and molecules,
Advances in Atomic, Molecular and Optical
Physics, vol. 44, Academic Press 2001.

• First observed temperature dependence of DEA
  studied in O-/O2. Later DEA in CO2, N2O, H2, D2,
  HCl, DCl, HF, Na2, CCl4, CCl2F2,

Henderson, Fite and Brackmann, Phys.Rev. (1969)
183 157
Brüning et al. (1998) Chem. Phys. Lett. 292 177
Spence and Schulz, Phys. Rev. (1969) 188 280
20
Temperature dependence H2 case
E (4eV) H2(v) H2- H H -
Very strong CS dependence on internal
ro-vibrational excitation and also isotope
effect!
Allan and Wong, PRL (1978) 41 1791
Theoretical CS for DEA in H2(v, J0) (Horacek et
al. 2004) (o) and DEA CSs to some molecules from
Christophorou et al., 1984.
Very strong temperature dependence of DEA also in
HCl, DCl and HF.(Allan and Wong, 1981).
21
Temperature dependence DEA to excited target

• 14 eV H-/H2D-/D2 Cadež et al., J.Phys.B.
  (1988) 21 3271 Hall et al. PRL (1988) 60 337,
  Schermann et al., J.Chem.Phys. (1994) 101 8152

Markelj and Cadež, J. Chem. Phys. (2011) 134
124707
22
DEA to electronically excited target
Also to specific vibronic states of SO2 Kumar
et al. Phys. Rev. A (2004) 70 052715.
O-/O2 Belic and Hall, J.Phys.B (1981) 134
124707.
DEA in SO2 Krishnakumar et al., Phys. Rev. A
(1997) 56 1945.
23
The way of experimental development

• Some mistakes are indispensable on the way and
  they contribute to the charm of scientific
  development!
• no temperature dependence of CS in H2
• C2H2 second peak C- ? H-
• CS for H-/CH4
• Signal background (H-/H2, D-/D2)
• Influence of electron energy resolution, momentum
  transfer, target gas temperature on experimental
  result.
• Total clearness of results and perfect agreement
  between the theory and experiment is an ultimate
  goal but the quest for this goal is sometimes a
  way to errors.

24
The way of experimental development
Transfer of the momentum of incident electron to
the target is often overseen although it is not
negligible in modern momentum imaging it is
clearly visible and normally taken into account.
25
DEA theoretical description
There are two energy manifolds one for the
neutral target molecule and another for compound
negative ion. Particle, that connects these two
manifolds is electron basically, satiation is
similar to what one has in elementary particle
physics!

• The theory describes different aspects of
  resonant electron-molecule collision
• Energy levels of neutral molecules (common for
  all molecular spectroscopy).
• Energy levels of negative ion compound molecule
  (unstable!) both real part and decay width. For
  both cases energy levels are function of
  molecular shape parameters (bond lengths and bond
  angles).
• Time evolution of compound molecule typically
  on fs level.
• Extraction of cross sections for particular
  decay channel, resonant scattering and DEA.

26
DEA theoretical description

• First theories were taken from, then, more
  advanced nuclear physics.
• Later, very sophisticated theories developed for
  molecular resonances
• Local complex potential - resonant state
  dependent only on R.
• Non-local complex potential resonant state
  dependent on R and Ee.
• Wave packet propagation in local complex
  potential.
• Ab initio calculations of compound state
  parameters.

27
DEA theoretical description
DEA in polyatomic molecules C2H2

• Recent detailed theoretical analysis of
• DEA in acetylene e C2H4 ? C2H- H
• Chourou and Orel, Phys.Rev.A (2008) 77 042709

28
Applications and needs

• Where is DEA present?
• As a binary collision process in rarefied media
  where free electrons are present.
• The basic physical mechanism of DEA resonant
  electron capture to a molecule and subsequent
  bond breaking, occurs also on surfaces and in
  dense media.
• The later relevance drives main interest for DEA
  in the present time!

29
Applications and needs
DEA in rarefied media - Modelling of ionized
gases (BF3, SF6, CH4, SiH4, )

• Particular example fusion plasma
• Relatively small number of molecular species in
  edge plasma but still relevant process H2, D2,
  T2, HD, HT, DT and also hydrocarbons
  satisfactory data base exists (e.g. http\\www.
  eirene.de Juel Reports 3966, 4005, 4038, 4105
  R. K. Janev, D. Reiter and U. Samm).
• New development due to ITER material mix (Be and
  W compounds) but in particular processes with
  nitrogen N2, NH3, and isotopologues.
• Besides being important for the plasma
  properties, it is potentially relevant to
  specific collision processes related to impurity
  transport and interaction with surfaces
  deposition and desorption).

30
Sensitivity on vibrational excitation of H2 from
the wall1-D Monte-Carlo model for neutral
particle transport (Kotov and Reiter, 2005)
H2(v) from the wall to edge plasma
All H2 from the wall in v4
All H2 from the wall in v0
1017 m-3 lt ne lt 1020 m-3, 1eV lt Te lt 100 eV, 10-3
ne lt nI lt 10-1ne, nHo 10-3ne
31
Applications and needs
Rarefied media Volume H- (D-) ion sources
This is a classic example of application of DEA
for plasma development
From M. Bacal, Nuclear Fusion 46 (2006) S250
32
Applications and needs
Rarefied media Volume H- (D-) ion sources

• Vibrationally excited H2 are precursor for H- ion
  production by DEA
• They are produced by
• e-V H2 e (slow) ? H2(X 1Sg, v) e
• E-V H2 e (fast) ? H2(B 1Su,C 1Pu) ? H2(X
  1Sg, v) hn
• Cascade H2(X 1Sg, v0) e ? H2(E, F 1Sg)
• ? H2(B 1Su) ? H2(X 1Sg, v) hn
• Recombinative desorption H H wall ? H2(X
  1Sg , v 1, 2)
• followed by the E-V excitation of the X1Sg
  state with the low v
• H2(X 1Sg, v 1, 2) e (fast) ? H2(B 1Su,C
  1Pu) ?
• H2(X 1Sg, v ? 1, 2) hn

From M. Bacal, Nuclear Fusion 46 (2006) S250
33
Applications and needs
Rarefied media - Sensitive gas detectors
READ Reversed Electron Attachment Detector
Low energy electron attachment is very efficient
to producing characteristic anions for low level
pollution monitoring.
From Boumsellek and Chutjian. 1992 and Darrach
et al. 1998
34
Applications and needs
Rarefied media - Aeronomy and astrochemisty (from
Earth and other planetary atmospheres to
cosmology)

• DEA is potentially important in the environments
  where low energy electrons are present and
  neutral molecules and radicals mainly indirect
  evidence from modelling.

L. Campbell and coworkers have been showing the
importance of accurate data on e-molecule
collisions for actrochemistry modelling.
35
gt160 Interstellar Molecules
The number of molecular species observed in
various regions in space is steadily increasing
2 3 4 5 6 7 8 9 10 11
H2 C3 c-C3H  C5 C5H  C6H  CH3C3N  CH3C4H  CH3C5N?  HC9N 
AlF  C2H l-C3H  C4H l-H2C4 CH2CHCN  HCOOCH3 CH3CH2CN  (CH3)2CO 
AlCl  C2O C3N  C4Si C2H4  CH3C2H  CH3COOH  (CH3)2O  NH2CH2COOH ? 12
C2 C2S C3O  l-C3H2 CH3CN HC5N  C7H CH3CH2OH  C6H6
CH  CH2 C3S  c-C3H2 CH3NC  NH2CH3 H2C6 HC7N 
CH  HCN C2H2 CH2CN CH3OH HCOCH3 CH2OHCHO  C8H  13
CN HCO CH2D ?  CH4 CH3SH  c-C2H4O  HC11N
CO HCO HCCN  HC3N HC3NH  CH2CHOH  PAHs
CO HCS HCNH  HC2NC HC2CHO  C60
CP HOC HNCO HCOOH NH2CHO
CSi  H2O HNCS  H2CHN C5N 
HCl  H2S HOCO  H2C2O
KCl  HNC H2CO H2NCN
NH HNO H2CN  HNC3
NO  MgCN H2CS SiH4
NS  MgNC H3O H2COH
NaCl N2H NH3
OH N2O SiC3
PN  NaCN
SO OCS
SO  SO2
SiN  c-SiC2
SiO  CO2
SiS  NH2
CS H3
HF SiCN
SH FeO AlNC
National Radio Astronomy Observatory,
(http//www.cv.nrao.edu/awootten/allmols.html
(Adapted from N. J. Mason, 2010)
36
Role of anions - data needs for modelling
Hydrocarbon anions are observed in different
environments in space (e.g. Millar et al., 2007,
HaradaHerbst, 2008) and detailed modelling of
these requires data for various processes.

• Result of modeling of the time evolution of CnH
  and CnH- following the evaporation of methane ice
  as applied to explain the observations from
  L1527, an envelope of a low-mass star-forming
  region - from HaradaHerbst, 2008.

Recent relevant study of DEA in H-CC-CC-H by
May et al. PR A 77, 040701R (2008) and on RVE by
Allan et al., PR A 83, 052701 (2011)
37
Planetary atmospheres Titans in particular
Composition 97 N2 2 CH4 1 C2H2,
C2H4,.Ar(?)
38
Role of anions - data needs for modelling
V. Vuitton et al., Negative ion chemistry in
Titans upper atmosphere, Planetary and Space
Science 57 (2009) 15581572

• - The Electron Spectrometer (ELS), revealed the
  existence of numerous negative ions in Titans
  upper atmosphere.
• Up to 10,000 amu/q, two (three) distinct peaks
  at 22 4 and 44 8 (and 82 14 ) amu/q,
• Ionospheric model of Titan including negative
  ion chemistry.
• DEA mostly to HCN initiate the chain of
  reactions.

- Radiative electron attachment is fast for
bigger carbon chain molecules as for C6H but very
slow for light ones. - Anions from thermal energy
electron capture not taken into account. - Data
for DEA are used (CH4,C2H2, estimate for C4H2 and
C6H2. - Ion pair production by photons (but not
by electrons) - Photo-detachment, cation-anion
recombination, anion-neutral associative
detachment. - Proton transfer is very efficient
(e.g. H- C2H2 ?C2H- H2). - Polymerization
(e.g. C2nH- C2H2 ? C2n2H- H2).
39
Low energy H- yield from DEA to small hydrocarbons

• Potential relevance of DEA to small hydrocarbons
  stimulated an experimental study of the low
  energy H- ion yield from some small HCs.
• Two processes contribute
• - Dissociative electron attachment for Ee lt15 eV
• Polar dissociation (ion pair production) for Ee
  gt 15 eV.
• Activity within COST CM0805 The Chemical cosmos

Cadež, Rupnik and Markelj, Eur. Phys. J. D
(2012) 66 73
40
Applications and needs
Dense media and surfaces

• Similar resonant states exist in molecules
  incorporated in dense media but their properties
  (energy, symmetry and lifetime) are modified
• - by substrate if adsorbed on the surface
• - by the close neighbor molecules (thick layers,
  clusters, in the bulk).
• Different scenarios occur regarding released
  anion from DEA - it can be emitted out of the
  system (e.g. condensed layers) or can induce
  further reactions.

41
DEA at surfaces dense layers

• Group of R. E. Palmer at the University of
  Birmingham molecule manipulation by STM at room
  temperature

Selective dissociation of chlorine atoms from
individual oriented chlorobenzene molecules
adsorbed on a Si(111)- 7x7 surface at room
temperature.
Proposed two electron mechanism first electron
(b) excites C-Cl wag vibrations (c) and second
electron (d) induce dissociation of C-Cl bond.
Free Cl sticks to the surface (e).
Some public titles following the paper in Nature
(Google) - Quantum electron submarines help
push atoms - (New Scientist) - Nano-surgeons
break the atomic bond (The Telegraph) -
Birmingham Scientists Witness the Birth of an
Atom
Sloan and Palmer, Nature 434 (2005) 367
42
DEA at surfaces dense layers

• Group of L. Sanche, Univ. of Sherbrooke, Quebec,
  Canada
• Group of R. Azria, A. Lafosse , UPS, Orsay,
  France

Lafosse et al., Phys. Chem. Chem. Phys. 8 (2006)
55645568
D- from amorphous ice at 190 K Simpson et al.,
J.Chem.Phys. 107 (1997) 8668
43
DEA in biomolecules
Radiation Damage Electron driven rections
Thymine
(From E. Illenberger, 2007)
44
DEA in biomolecules
F. Martin, P. D. Burrow, Z. Cai, P. Cloutier, D.
Hunting, and L. Sanche, PRL 93 (2004) 068101
45
Data production and needs
Data collection, evaluation and recommendations
Data production
Needs
Data formatting DATABASE
Users Modelling
Sensitivity analysis
46
Data production and needs

• Data production
• Experiments of light
• (more individual work)
• - new processes
• - basic properties
• - benchmark cases
• - new exp. methods
• Experiments of fruit
• (more collective work)
• - choice of subject
• - application of methods
• - data production
• Interpretation of data
• Theory
• - In-depth explanation of processes
• - development of models

Data shaping Formation of standardised data
bases Appropriate data formats Accessibility
Data evaluation Collection from all available
sources, new and old. Evaluation of applied
methods and claimed accuracy. Recomdation of
best data to be used. Feedback with data
producer. Recommendations for new measurements
or calculations.
Data usage Modelling of complex processes, new
technological procedures, processes in other
sciences. Sensitivity analysis Feedback to data
producers.
47
Current activities
List of laboratories actively participating in
present DEA research Sherbrooke, Canada (Léon
Sanche, biomolecules, surfaces, experiment,
theory) Lincoln, Nebraska (Paul Burrow, Gordon
Gallup, experiment Ilya Fabrikant, 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) Innsbruck (Paul
Scheier, Tilmann Märk, Stefan Denifl,
biomolecules, collisions in He nanodroplets) Fribo
urg (Michael Allan) Berlin (Eugen Illenberger,
biomolecules) Open University, Milton Keynes
(Nigel Mason, Jimena Gorfinkiel, experiment,
theory) Bratislava, Slovakia (Štefan
Matejcik) University of Podlasie, Poland (Janina
Kopyra, electron transport) Prague, Charles
University (Jirí Horácek, Martin Cížek, Karel
Houfek ( Wolfgang Domcke), theory) Orsay (Robert
Abouaf, Roger Azria, Ann Lafosse,
surfaces) London (JonathanTennyson, R-matrix
theory) Island (Oddur Ingólfsson,
experiment) Tata Institute, Mumbai (E.
Krishnakumar, S. V. K. Kumar, V. Prabhudesai,
experiment velocity slice imaging) Hefei, China
(S. X. Tian, B. Wu, experiment velocity slice
imaging) (adapted from M. Allan, ICPEAC, 2011)
48
Available data

• List is too long to be presented here only
  examples
• Diatomic H2, O2, CO, NO, S2, Cl2, Br2, HF, HCl,
  HBr
• Triatomic H2O, CO2, CS2, H2S, O3, SO2, N2O, NO2,
  HCN
• Small polyatomic CH4, NH3, BF3, C2H2, CCl2F2,
  C6H6, SF6, many chloro- and fluorocarbons, CH3CN,
  N2O5
• Big molecules C60, HCOOH, C2H5NO2, uracil,
  glicine, nitrotoluene, cyclopentanone,
  tetrahydrofuran,
• HFFA (CF3)2CN-NC(CF3)2), tymine, various
  molecular clusters

49
Perspectives

• More data on DEA to excited molecules (both,
  ro-vibrational and electronic) are needed.
• Angular distribution of ions from DEA to larger
  molecules and experiments on oriented targets.
• Resonances (and DEA) in EB field.
• Applications in future might be related to well
  defined time scale of e-impact induced molecular
  breakdown.
• DEA in dense media is a separate field of
  research of high importance with its own new
  experimental and theoretical development.

50
Collaborations on DEA and acknowledgement

• Milan Kurepa
• Ratko Janev
• Aleksandar Stamatovic
• Vlada Pejcev
• Florance Fiquet-Fayard
• Richard Hall
• Catherine Schermann
• Nada Djuric
• Will Castleman
• Sabina Markelj
• Nigel Mason
• E. Krishnakumar

51
Some references

• R. E. Palmer and P. J. Rous, Resonances in
  electron scattering by molecules on surfaces,
  Rev. Mod. Physics 64 (1992) 383
• S Matejcik, A Kiendler, P Cicman, J Skalny, P
  Stampfli, E Illenberger, Y Chu, A Stamatovic and
  T D Mark, Electron attachment to molecules and
  clusters of atmospheric relevance oxygen and
  ozone, Plasma Sources Sci. Technol. 6 (1997) 140
• A. CHUTJIAN, A. GARSCADDEN, J.M. WADEHRA,
  ELECTRON ATTACHMENT TO MOLECULES AT LOW ELECTRON
  ENERGIES, Physics Reports 264 (1996) 393-470
• Savin et al. (14authors) The impact of recent
  advances in laboratory astrophysics on our
  understanding of the cosmos, Rep. Prog. Phys. 75
  (2012) 036901
• M. Bacal, Physics aspects of negative ion
  sources, Nucl. Fusion 46 (2006) S250S259
• L.G. Christophorou , D. Hadjiantoniou, Electron
  attachment and molecular toxicity, Chemical
  Physics Letters 419 (2006) 405410