1 / 41

ELECTRON - COLD MOLECULAR ION REACTION USING THE HEAVY ION STORAGE RING TECHNIQUE

ELECTRON - COLD MOLECULAR ION REACTION USING THE HEAVY ION STORAGE RING TECHNIQUE. Daniel Zajfman Weizmann Institute of Science Israel and Max-Planck Institute for Nuclear Physics, Heidelberg. AB +. V=2. V=1. V=0. Production of cold molecules and molecular ions. V(R).

maren
Download Presentation

ELECTRON - COLD MOLECULAR ION REACTION USING THE HEAVY ION STORAGE RING TECHNIQUE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ELECTRON - COLD MOLECULAR ION REACTION USING THE HEAVY ION STORAGE RING TECHNIQUE Daniel Zajfman Weizmann Institute of Science Israel and Max-Planck Institute for Nuclear Physics, Heidelberg

  2. AB+ V=2 V=1 V=0 Production of cold molecules and molecular ions V(R) Molecular ion production in standard ion sources: Vibrationally excited AB • Cooling Techniques: • Supersonic expansion. • Cold buffer gas collisions. • Trapping. V=0 Typical time scales: 10 ms – 10’s seconds R

  3. The Test Storage Ring (TSR) MPI - Heidelberg Detectors (neutrals) Ion source H2+ / HD+ , HeH+, He2+, H3+... C6+ ... Fe23+ ~0.2 ... 8 MeV/u Electron target Electron collisionmeasurement Electron target ~0.5 ... 8 keV Dissociative Recombination AB+ + e- A + B Electron cooler

  4. Typical setup: Merging the molecular ion beam with the e--beam AB+ + e- A + B Ion beam 1.5 m

  5. Electron-cold molecular ion reaction: Dissociative Recombination Merged Beam Kinematics Electrons Ee,me Ions Ei, mi Center of mass resolution: ~ meV resolution for zero relative kinetic energy!

  6. Ion Orbit Electron Target Electron cooler Injection Beamline Hot Molecular Ions MPI-K Heidelberg

  7. TSR electron cooler TSR dipole Correction dipoles Acceleration section Interaction section electron beam Toroid Collector Rails Ion beam High resolution electron target at TSR

  8. Cryogenic Photocathode Driven Electron Beam. T~500 μeV • Laser Power: 1 W (800 nm) • Quantum yield of fully activated cathode: 31% • Extracted current: 0.25 mA (1 mA is feasible) • Cathode stability: 10-16 hours • Transverse electron temperature after • magnetic expansion: 500 μeV (5K) D. A. Orlov et al.,Appl. Phys. Lett. 78, 2721 (2001) 2D photoelectron spectroscopy (E|| , E ) 90 K 300 K

  9. Electron-cold molecular ion reaction: Dissociative Recombination HD+ + e- H(n) + D(n’) + KER Indirect process Direct process Interference Rydberg state e- Kinetic Energy Release H(1s)+D(2l) D(1s)+H(2l)

  10. Dissociative recombination cross section for HD+ (hot) Before 1992 No storage Vibrationally excited HD+

  11. kTperp =500 μeV, kTpar=20 μeV June 1992 June 2004 P. Forck et al Cryring (2001) Trot=300 oK Dissociative recombination cross section for HD+ (cold) HD+ + e- H+D D. Orlov, F. Sprenger, M. Lestinski, H. Buhr, L. Lammich, A. Wolf et al.

  12. Low-energy rovibrational resonances (ℓ = 0, 2 → ΔJ = 0, ± 2, ± 4) HD+ (1sσ, v = 0, J ) + e → HD** (1sσnℓλ ,v'J' ) → H + D MQDT: Ioan Schneider and F. O. Waffeu Tamo (LeHavre) (calculations in progress) v = 4, n = 4 v = 1, n = 8

  13. Eb D Dynamics of the dissociative recombination of HD+(v=0) Ee Ek 3D fragment imaging

  14. Branching ratio in the Dissociative Recombination of HD+ as a function of electron energy. Full line: Landau-Zener model with known coupling constants between the neutral states. Strongly anisotropic, and electron energy dependent!

  15. Lithium chemistry of the early universe First galaxies and stars were formed from H, He, and trace amounts of D and Li. Radiative cooling at T<8000 K is controlled by the presence of a small fraction of the gas that is molecular. It is molecular cooling that allows primordial clouds to collapse. Molecules with large dipole moment are the most effective coolant. HeH, HeH+, LiH, LiH+ Primordial Li, Li+, LiH, and LiH+ abundance ? Molecular Physics Nucleosynthesis

  16. Dissociative recombination Stancil, Lepp and Dalgarno, ApJ., 458, 401 (1996)

  17. cm3.s-1 LiH+ Dissociative Recombination Rate Coefficient Stancil, Lepp and Dalgarno, ApJ., 458, 401 (1996)

  18. LiH+ + e-  Li + H LiH+ No crossing between neutral states and ionic states.  Low recombination rate coefficient.

  19. Exp. setup on the TSR. LiH+ + e-  Li + H Rate of neutral fragments on the detector The absolute rate coefficient can be extracted from the different lifetimes.

  20. DR cross section LiH+ + e-  Li + H At T=300 K: =(2.70.9)x10-7 cm3/s (previous assumed value: =2.6x10-8 cm3/s ) S. Krohn et al., PRL, 4005, 86 (2001). What is the mechanism behind the DR process in this case?

  21. DR is now the fastest process. What are the effects on the early Universe Chemistry? Dissociative recombination 2.7-7 =(2.70.9)x10-7 cm3/s Stancil, Lepp and Dalgarno, ApJ., 458, 401 (1996)

  22. Cosmic rays H2 + H2+→ H3+ + H H3+ rovibrational lines Cold free-electron interactions H + H + H H3+ + e DR H2 + H Dissociative recombination of H3+ Astrophysical observations Temperature: ~50 K Density: 101...103 cm-3 Abundance of H3+ in diffuse interstellar medium Infrared absorption against Cygnus OB2 12 McCall et al. Science 279, 1910 (1998); Astrophys. J. 567, 391 (2002) For DR rate coefficient of 10-7 cm3 s-1: Observed column density~102 – 103 larger than modeled

  23. H3+ Dissociative recombination rate coefficient: 1947-2005 H3+ cannot be thermalized in a storage ring. Most recent theoretical results, including Jahn-Teller coupling (C. Greene et al.) Theory Infrared absorption Experimental data Merged beams (single pass) Storage rings

  24. Dissociative recombination of H3+ Remote curve crossing H3+ Electron capture viaJahn-Teller coupling of electronic and ro-vibrational motion H3* 75% 25% Prototype system for electron capture and dissociation mechanisms in polyatomic species Symmetric deformation Equilateral

  25. What happen to the rotational population when you store a hot H3+ in a ring? Simulation of radiative rotational transitions for H3+ starting from Trot= 0.23 eV, and calculating 245,000 transitions (J. Tennyson web-site). Calculations L. Neale, et al., Astrophys. J., 464, 516, (1996) B. M. Dinelli, et al., J. Mol. Spectr. 181, 142 (1997)

  26. Is the additional energy stored as rotational energy? Simulation of radiative rotational transitions for H3+ starting from Trot= 0.23 eV, and calculating 245,000 transitions (J. Tennyson web-site). Computer simulation Long live states: States for which the axis of rotation is nearly parallel to the C3v symmetry axis (K=J, K=(J-1)) J: Angular momentum K: Projection of J onto the molecular symmetry axis

  27. Storage ring experiments with rotationally cold H3+ Long lived rotational levels in H3+ Radiatively stable state Ortho-H3+ (I = 3/2) Para-H3+ (I = 1/2) ΔE = 2.9 meV (33 K) - Need cold (10 K) ion source - Lowest states of different spin symmetry

  28. Pre-trapping for Pre-cooling Production of rotationally cold H3+ at the TSR Done first at CRYRING using supersonic expansion H. Kreckel et al. (2004)

  29. ve = vi Stored H3+ ion beam from cryogenic RF trap Energy dependence of H3+ recombination TSR HeidelbergCryogenic H3+ ion trap (T ~ 15 K) Photocathode electron beam Electron temperature: ~ 5 K TSR B. J. McCall et al., Nature 422, 500 (2003) H. KreckelM. MotschJ. Mikosch D. Orlov M. Lestinsky

  30. ve = vi Stored H3+ ion beam from cryogenic RF trap Energy dependence of H3+ recombination TSR HeidelbergCryogenic H3+ ion trap (T ~ 15 K) Photocathode electron beam Electron temperature: ~ 5 K Theory:Kokoouline, Greene H. KreckelM. MotschJ. Mikosch D. Orlov M. Lestinsky

  31. ve = vi Para/Ortho 50:50 Para/Ortho 100:0 Stored H3+ ion beam from cryogenic RF trap Energy dependence of H3+ recombination TSR HeidelbergCryogenic H3+ ion trap (T ~ 15 K) Photocathode electron beam Electron temperature: ~ 5 K Theory:Kokoouline, Greene H. KreckelM. MotschJ. Mikosch D. Orlov M. Lestinsky

  32. Measuring branching ratio All of them produce a full energy signal on the detector! Also: translucent grid The grid method: How to distinguish between a molecule and two independent atoms? molecule two atoms molecule two atoms Detector Detector Detector Detector Eb Eb Eb Eb Grid (T) Grid (T) E E E E Eb Eb Eb Eb

  33. (O,H,H) (O,H) (O) T=63% Grid transmission T=28%

  34. Branching ratio for the dissociative recombination of polyatomics with low energy electrons: H3+ CH2+ H2O+ NH2+ PH2+ Cryring (Stockholm) and Astrid (Aarhus) results Three body dissociation is dominant (60-80%) Datz, Phys. Rev. Lett. (1995) Not true for higher energy electrons

  35. Electron Induced Rotational Excitation and De-Excitation Rotational cooling Super Elastic Process (SEC) HD+(v=0,J) +e-(Ek)  HD+(v=0,J’) + e-(E’k) (J’<J; E’k>Ek) HD+(J) + e-  H + D + (E) “Pump-Probe” experiment with two electron beams Probing (DR) Rotational cooling

  36. This is NOT an experimental proof of rotational cooling via SEC processes Fitting the rotational tail using the theoretically known DR rate coefficients (I. Schneider, in progress)

  37. Radiative cooling Radiative + DR cooling Radiative + DR +SEC SEC=1.5x10-7 cm3/s Solving the Master equation for the rotational population with radiative cooling only Experiment Solving the Master equation for the rotational population with radiative transition DR “depletion”, and Super-Elastic Collision (SEC) Solving the Master equation for the rotational population with radiative transition and DR “depletion”

  38. The present storage ring technology “limits” the physics to vibrational ground state molecular ions To achieve rotational cooling, the ring needs to be cooled to much lower temperature (~10 K) Outlook Physics with rotationally cold molecular ions: “real” interstellar conditions The Cryogenic Storage Ring CSR

  39. The Next Generation of Storage Ring: The Cryogenic Storage Ring (CSR) Merged neutral atomic beam Ultra cold electron beam Reaction microscope

  40. German-Israeli Foundation for Fundamental Research (GIF) Ion Storage and Molecular Quantum Dynamics Weizmann Institute of Science Rehovot, Israel Max-Planck-Institut für Kernphysik Heidelberg, Germany D. Strasser Y. Nevo Y. Toker O. Heber D. Shafir H. Rubinstein A. Wolf D. Schwalm H. Kreckel L. Lammich H. B. Pedersen V. Andrianarijaona S. AltevogtH. Buhr S. Altevogt S. Novotny M. Motsch Univ. Louvain-la- Neuve, Belgium X. Urbain Univ. Paris Sud Univ. du Havre France (Theory) I. Schneider, A. Suzor-Weiner M. Lestinsky F. Sprenger D. A. Orlov U. Weigel M. Grieser R. von Hahn R. Repnow Electron target TU Chemnitz, Germany Photocathode D. Gerlich TSR and accelerator European Research Network“Electron transfer reactions” (2000–04)

More Related