Electron-cold molecular ion reactions using - Nobel Symposium 133

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Electron-cold molecular ion reactions using  - Nobel Symposium 133 Powered By Docstoc
					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
           Production of cold molecules and molecular ions


                                              P(v)  AB ( R) AB ( R)

                                V(R)
                                                      AB+
     Molecular ion production          V=2         Vibrationally excited
     in standard ion sources:           V=1
                                        V=0




                                                         AB
 Cooling Techniques:
 Supersonic expansion.
 Cold buffer gas collisions.                      V=0
 Trapping.

Typical time scales:                                          R
10 ms – 10’s seconds
     Detectors              The Test Storage Ring (TSR)
     (neutrals)
                                 MPI - Heidelberg

                                                               Ion source


                                                        H2+ / HD+ , HeH+, He2+,
                                                        H3+ ... C6+ ... Fe23+


                                   Electron target       ~0.2 ... 8 MeV/u
Electron target




                                   Electron collision
                                     measurement
                  ~0.5 ... 8 keV




                                                             Dissociative
                                                            Recombination
                                                           AB+ + e-  A + B


                           Electron cooler
Typical setup: Merging the molecular ion beam with the e--beam




                                      AB+ + e-  A + B




                                                         Ion beam




                                            1.5 m
Electron-cold molecular ion reaction:
                                               Merged Beam Kinematics
Dissociative Recombination


                             Electrons Ee,me
  Ions Ei, mi




                                                       2
                          1          me         
                   Ecm    me vcm  
                               2
                                         Ei  Ee 
                          2          mi         

  Center of mass resolution:
                                        2                   2   1/2
                     v  m
                                             vi           
                                                                
           ΔEcm     1  
                      
                            e
                               m ΔEi    1  v ΔEe 
                                 e
                                                              
                        vi  i              e           
                                                               

          ~ meV resolution for zero relative kinetic energy!
                          Electron Target           Ion
        Electron cooler                             Orbit




                             Injection
                             Beamline
                                            Hot Molecular Ions


MPI-K Heidelberg
             High resolution electron target at TSR


TSR electron cooler


                        TSR dipole




                              Acceleration section        Correction dipoles

                                                                 Interaction
                                     electron beam                 section
                                                                    Toroid



                                                     Collector
                      Rails
                                                                          Ion beam
                 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 )
                                  300 K                        90 K
     Electron-cold molecular ion reaction: Dissociative Recombination

                        HD+ + e-  H(n) + D(n’) + KER

                                             HD+ (2p )
                                                      u


Indirect process                                                    Direct process




                              Interference
                                                    Rydberg state
                                       HD+ (2 +)
                         e-                    g

     Kinetic
     Energy
     Release
                                                                    H(1s)+D(2l)
                                                                    D(1s)+H(2l)
                Dissociative recombination cross section for HD+ (hot)
Before 1992

   No storage                 Vibrationally excited HD+
   Dissociative recombination cross section for HD+ (cold)


                       HD+ + e-  H+D

                                              kTperp =500 μeV, kTpar=20 μeV
                                                               June 1992
                                                             June 2004

                                                   Cryring
                                                   (2001)
                                                               P. Forck et al




       Trot=300 oK




D. Orlov, F. Sprenger, M. Lestinski, H. Buhr, L. Lammich, A. Wolf et al.
             Low-energy rovibrational resonances
                                               (ℓ = 0, 2 → ΔJ = 0, ± 2, ± 4)

HD+ (1sσ, v = 0, J ) + e → HD** (1sσ nℓλ , v'J' ) → H + D
         MQDT: Ioan Schneider and F. O. Waffeu Tamo (LeHavre)
                         (calculations in progress)
                                               v = 4, n = 4




       v = 1, n = 8
                                                           +
           Dynamics of the dissociative recombination of HD (v=0)

HD   e -  H(1s)  D(n)




           Ee

                                                                Ek



                                                          3D fragment imaging

                                                         Eb




                                                                     D
  Branching ratio in the
  Dissociative Recombination
  of HD+ as a function of
  electron energy.



                     H(1s)  D(nl)
HD (v  0)  e (E)  
                

                     D(1s)  H(nl)


  Full line: Landau-Zener model
             with known coupling
             constants between the
             neutral states.

       Strongly anisotropic, and electron
         energy dependent!
                   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 ?


                                     Nucleosynthesis           Molecular Physics
Dissociative
recombination




                Stancil, Lepp and Dalgarno, ApJ., 458, 401 (1996)
            LiH+
Dissociative Recombination
     Rate Coefficient


                                              cm3.s-1




           Stancil, Lepp and Dalgarno, ApJ., 458, 401 (1996)
                      LiH+ + e-  Li + H


                                   LiH+




No crossing between
neutral states and
ionic states.
 Low recombination
rate coefficient.
                                             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.
                                                              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?
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)
                      Dissociative recombination of H3+
                                 Astrophysical observations

 Abundance of H3+ in diffuse interstellar medium              Temperature: ~50 K
                                                              Density:      101...103 cm-3


    Infrared absorption against Cygnus OB2 12

                                                          Cosmic rays


                                                              H2 + H2+ → H3+ + H

              H3+ rovibrational lines




   McCall et al. Science 279, 1910 (1998);
   Astrophys. J. 567, 391 (2002)
                                                       Cold free-electron interactions

For DR rate coefficient of 10-7 cm3 s-1:                                  H + H + H
                                                          H3+ + e
        Observed column density                                DR          H2 + H
     ~102 – 103 larger than modeled
       H3+ Dissociative recombination rate coefficient: 1947-2005

                                                  H3+ cannot be thermalized
                                                  in a storage ring.



                                  H2 (v)  H(1s)
                     
                    H3  e   
                               H(1s)  H(1s)  H(1s)

                                                  Most recent theoretical
                                    Theory        results, including Jahn-Teller
                                                  coupling (C. Greene et al.)




                  Infrared absorption
Experimental data Merged beams (single pass)
                  Storage rings
                      Dissociative recombination of H3+


                                         Remote curve crossing

      H3+


      H3*                                Electron capture via
                                         Jahn-Teller coupling of
                                         electronic and ro-vibrational
                            75%          motion

                            25%



Symmetric deformation                   Prototype system for electron
                                        capture and dissociation
                                        mechanisms in polyatomic species
        Equilateral
      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)
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
            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
                  Production of rotationally cold H3+ at the TSR
Done first at CRYRING
using supersonic expansion
                                                  Pre-trapping for
                                                  Pre-cooling




                                                             H. Kreckel et al. (2004)
     Stored H3+ ion beam from cryogenic RF trap
Energy dependence of H3+ recombination
             TSR Heidelberg
    Cryogenic H3+ ion trap (T ~ 15 K)
       Photocathode electron beam
       Electron temperature: ~ 5 K


                        TSR
                                          ve = vi
 B. J. McCall et al.,
 Nature 422, 500
 (2003)



                                            H. Kreckel
                                            M. Motsch
                                            J. Mikosch

                                            D. Orlov
                                            M. Lestinsky
    Stored H3+ ion beam from cryogenic RF trap
Energy dependence of H3+ recombination
             TSR Heidelberg
    Cryogenic H3+ ion trap (T ~ 15 K)
       Photocathode electron beam
       Electron temperature: ~ 5 K


                             Theory:
                             Kokoouline, Greene   ve = vi




                                                    H. Kreckel
                                                    M. Motsch
                                                    J. Mikosch

                                                    D. Orlov
                                                    M. Lestinsky
    Stored H3+ ion beam from cryogenic RF trap
Energy dependence of H3+ recombination
             TSR Heidelberg
    Cryogenic H3+ ion trap (T ~ 15 K)
       Photocathode electron beam
       Electron temperature: ~ 5 K



                                                       ve = vi
                              Para/Ortho 50:50 Theory:
                              Para/Ortho 100:0 Kokoouline, Greene



                                                         H. Kreckel
                                                         M. Motsch
                                                         J. Mikosch

                                                         D. Orlov
                                                         M. Lestinsky
                            Measuring branching ratio


                                    Α  Β  C α
                                                                  All of them produce
             ΑΒC (v)  e  (Εe )   ΑΒ  C β                     a full energy signal
                                                                   on the detector!
                                     ΑC  Β
                                              γ
                                                                        Also: translucent
                                                                              grid
The grid method:
How to distinguish between a molecule and two independent atoms?

molecule   Detector   two atoms              molecule                 two atoms Detector
                                  Detector              Detector



   Eb                     Eb                    Eb                       Eb
                                                        Grid (T)                  Grid (T)




           Eb   E                  Eb   E               Eb   E                    Eb   E
               OH  H                    (O,H,H)
              
H2O   e    O  H2
              O  H  H          (O,H)
                           (O)




                    T=63%


Grid transmission


                    T=28%
Branching ratio for the dissociative recombination of polyatomics
                      with low energy electrons:

H3+                                     Cryring (Stockholm) and Astrid (Aarhus) results
CH2+
H2O+    Three body dissociation is dominant (60-80%)
NH2+
PH2+

 Datz, Phys. Rev. Lett. (1995)



                                             Not true for higher
                                             energy electrons
         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
                                       Fitting the rotational tail using the
                                       theoretically known DR rate
                                       coefficients (I. Schneider, in progress)




This is NOT an experimental proof of
rotational cooling via SEC processes
              Experiment           Solving the Master equation
                                                Radiative cooling
                                   for the rotational population
                                   with radiative cooling only




                                  Solving the Master equation
                                             Radiative + DR +SEC
Solving the Master equation       for the rotational population
         Radiative population
for the rotational + DR cooling              SEC=1.5x10-7
                                  with radiative transition cm3/s
with radiative transition         DR “depletion”, and
and DR “depletion”                Super-Elastic Collision (SEC)
                       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
The Next Generation of Storage Ring: The Cryogenic Storage Ring (CSR)




                                                            Merged neutral
                                                            atomic beam
                                     Ultra cold
                                     electron beam



                                               Reaction
                                               microscope
               Ion Storage and Molecular Quantum Dynamics
Max-Planck-Institut für Kernphysik             Weizmann Institute of Science
Heidelberg, Germany                            Rehovot, Israel
                                         D. Strasser
                  A. Wolf                Y. Nevo
                  D. Schwalm             Y. Toker
                  H. Kreckel             O. Heber
                  L. Lammich             D. Shafir
                  H. B. Pedersen         H. Rubinstein
                  V. Andrianarijaona
                  S. Altevogt                               Univ. Louvain-la-
                  H. Buhr                X. Urbain          Neuve, Belgium
                  S. Altevogt
                  S. Novotny
                  M. Motsch              I. Schneider,      Univ. Paris Sud
                                         A. Suzor-Weiner    Univ. du Havre
 Electron target M. Lestinsky                               France (Theory)
                  F. Sprenger

 Photocathode     D. A. Orlov                               TU Chemnitz,
                  U. Weigel              D. Gerlich         Germany
 TSR and          M. Grieser
                  R. von Hahn          European Research Network
 accelerator      R. Repnow            “Electron transfer reactions” (2000–04)
                                       German-Israeli Foundation for
                                       Fundamental Research (GIF)

				
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