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1 Measuring and modeling absolute data for electron-induced processes Michael Allan Department of Chemistry University of Fribourg, Switzerland Chemistry.

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Presentation on theme: "1 Measuring and modeling absolute data for electron-induced processes Michael Allan Department of Chemistry University of Fribourg, Switzerland Chemistry."— Presentation transcript:

1 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

2 2 1.A very personal retrospective 2.H 2 : a short or long-lived resonance? 3.The peculiar story of threshold peaks : HF, HCl, HBr 4.CO 2 : threshold peaks are commonplace 5.H-C≡C-H : the necessity of many dimensions 6.HCOOH : the hybrid case 7.Higher energy : CH 3 OH, C 4 H 9 -O-C 4 H 9 etc. 8.Exotic molecules: Pt(PF 3 ) 4 9.Many excellent laboratories 10.Where do we find electron collisions ? 11.Conclusions Contents

3 3 gl oooooooo w in the dark Electron Tubes magic eye Pardubice

4 4 Basel M. Allan and J. P. Maier 1976 Energy of emitted photon Energy of incident electron

5 5 Yale M. J. W. Boness and G. J. Schulz 1976A. Stamatovic and G. J. Schulz 1970

6 6 short – lived radical anions = resonances background scattering resonant scattering coherent superposition  = 72°

7 7 Feshbach (  g ) 1 3s 2 valence core-excited (  g ) 1 (  u ) 2 Resonances: shape (  g ) 2 (  u ) 1 DEA and VE in H 2 “  * shape resonance” E threshold H - /H 2 D - /D 2 > 200 E (eV)

8 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...

9 9 Fribourg Very low background Low energy OK Wide energy range but Only relative units scattering angle only 0° and 180° no elastic scattering

10 10 Magnetic Angle Changer (Frank H. Read) Magnetic Angle Changer see also Andrew J. Murray, Wednesday lecture

11 11 Juraj Fedor, Olivier May, Dušan Kubala, Fribourg 2008 Time-of-Flight mass spectrometer for absolute DEA cross section

12 12

13 13

14 14 shape resonances core excited Feshbach resonance full-range spectrum in N 2

15 15 H 2 : a short or long-lived resonance?

16 16 E (eV) H 2 : a short or long-lived resonance? 1985 calculations: Čížek, Horáček, Domcke

17 17 looking at large R (high final v ) permits time resolution 1993

18 18 H 2  lifetime : going to the extreme D 2 :  = 2 ms Experiment : Golser et al., 2005 (Wienna)

19 19 Vibrational excitation in HF – naive expectation  * - resonance Threshold phenomena

20 20 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

21 21 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

22 22 structures everywhere

23 23 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)

24 24 Chemistry: Dissociative electron attachment to diatomic hydrides e  + HBr  H + Br 

25 25 Interchannel Coupling in Dissociative Atachment COMPARISON OF ABSOLUTE CROSS SECTIONS ! blue: nonlocal resonance theory red: absolute experiment Fedor May Allan (2008) Čížek Horáček Sergenton Popović Allan Domcke Leininger Gadea Phys. Rev. A 63 (2000) dissociative attachment cross section drops when a new vibrational excitation channel opens

26 26 to remember: long range (dipole) attraction  „nonlocal phenomena“ Vibrational Feshbach Resonances threshold peaks in VE large CS and steps in DEA

27 27 CO 2 has no dipole moment – is it like H 2 ? Fermi Resonance the (10 0 0) and (02 0 0) vibrations mix true states:{(10 0 0) + (02 0 0)} (Fermi dyad){(10 0 0) - (02 0 0)} two Raman lines

28 28 Excitation of the Fermi – split states is highly selective! Allan, Phys. Rev. Lett. 87 (2001) virtual state  * shape resonance Exciting the Fermi-dyad in CO 2

29 29 Allan, (2011, in print) Cross section for exciting the topmost member of the tetrad {(30 0 0), (22 0 0),... }

30 30 Similarity of vibrational cross sections in CO 2 and HF  D  D

31 31 Potential curves of CO 2 and HF Physica Scripta (2004) bending

32 32 Allan, J. Phys. B (2002)

33 33 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 Understanding the selectivity within the dyad

34 34 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

35 35 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

36 36 Dissociative Electron Attachment to Acetylene S. T. Chourou and A. E. Orel PRA 2008

37 37 Dissociative Electron Attachment to Acetylene S. T. Chourou and A. E. Orel

38 38 Chlorobenzene Skalický, Chollet, Pasquier, Allan, Phys. Chem. Chem. Phys. 2002

39 39 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 ring breathing C-Cl stretch

40 40 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 HCOOH + e   HCOO  + H

41 41 Vibrational excitation of formic acid

42 42 Vibrational excitation of formic acid - cusps, like HCl, HBr, HF

43 43 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

44 44  * anion  * anion neutral approach II

45 45 Dissociation of formic acid anion on the valence  * shape resonance potential surface DFT B3-LYP 6-31G * Isotope effect expected for D substitution on C-H

46 46 Isotope effect D. Kubala, O. May, M. Allan, 2011

47 47 Formic acid is a prototype for biomolecules : forms hydrogen bonds ! M Allan, Phys. Rev. Lett. (2007)

48 48 Similar situation in other biomolecules : uracil

49 49 Family III: higher energies On the complexity of dissociation via core-excited Feshbach resonances in polyatomic molecules

50 50 Feshbach resonances

51 51 photoelectron spectra are useful in predicting Feshbach resonances Bogdan Ibanescu 2007

52 52 O - C bond does not dissociate ! Bogdan Ibanescu 2007

53 53 Bogdan Ibanescu 2007 TD-DFT, pbe0/ g(3df,3p), geometry: DFT b3lyp/6-311+g(2df,2p) Rydberg states: potential curves

54 54 a recent example : Pt(PF 3 ) 4 (a FEBIP precursor)

55 55 Pt(PF 3 ) 4 : vibrational states

56 56 Pt(PF 3 ) 4 : fragmentation O. May, D. Kubala, poster Mo 038

57 57 Atoms great success of theory !

58 58 Absolute cross sections for excitation of the Ne (2p 5 3s) states at θ = 180°. M Allan, K Franz, H Hotop, O Zatsarinny and K Bartschat 2008 Ne

59 59 Some research groups active in electron collisions

60 60 Martin, Burrow, Cai, Hunting, Sanche, Phys. Rev. Lett Sanche and co-workers: slow electrons damage DNA Science, 2004

61 61 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

62 62 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

63 63 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

64 64 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

65 65 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

66 66 Where do we find electron – driven chemistry and physics?

67 67 - 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

68 68 · 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. Kushner University of Michigan Institute for Plasma Science & Engr. with permission GEC2010 Ref: Adapted from “Plasma Science: Advancing Knowledge in the National Interest”, US National Research Council, 2007.

69 69 Angle-integrated cross section for electron-impact excitation of the (6s6p) 3 P 0 o state of mercury from the (6s 2 ) 1 S 0 ground state. Resonance in Hg

70 70 SUCCESS AT CONTROLLING f(  ): PLASMA LIGHTING · Annual US electrical power consumption: 3.5 x 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. 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 Michigan Institute for Plasma Science & Engr. with permission

71 71 validate theory by comparing absolute (differential) cross sections for : - elastic scattering - vibrational - electronic - DEA Conclusions c.f. photochemistry

72 72 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 intersections H 2 O, CO 2 ; only beginning elastic scatteringvibrational excitationelectronic excitation experiment -full set of absolute cross sections measured for only few molecules -DEA : angular distributions -transient molecules (CF 2, metastables) -surfaces, liquids

73 73 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

74 74

75 75 Spin-orbit components of the NO ground electronic term Allan, Phys. Rev. Lett. (2004)

76 76 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

77 77 -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

78 78 Interchannel coupling in associative detachment dramatically influences product state distribution Živanov, Allan, Čížek, Horáček, Thiel, Hotop, Phys. Rev. Lett. (2002) associative electron detachment


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