Daniel Zajfman Max-Planck Institute for Nuclear Physics Heidelberg, Germany and Weizmann Institute of Science Rehovot, Israel Physics with Colder Molecular Ions: The Heidelberg Cryogenic Storage Ring CSR Robert von Hahn Manfred Grieser Carsten Welsch Dmitry Orlov Joachim Ullrich Jose Crespo Claus Schroeter Holger Kreckel Andreas Wolf Dirk Schwalm Michael Rappaport Xavier Urbain (LLN)

Characteristics of the Interstellar Medium and Many Body Quantum Dynamics CrossingBarrier Interstellar Conditions:  Low temperature  Low density o Slow reaction rates are also important. o Sensitive to the initial quantum states of the reactants

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

The Heavy Ion Storage Ring-MPI-Heidelberg AB + (hot, from the ion source) E=~ MeV Laser Coulomb Explosion Imaging AB + +X  ? Laser spectroscopy AB + +hv  ? Electron-molecular ion interaction AB + + e  ?

Vibrational cooling, the simplest case: HD + (H 2 + or D 2 + do not cool!) Internuclear distance (Å) How can we measure the vibrational population? HD + H 2 +, D 2 +

Coulomb Explosion Imaging: A Direct Way of Measuring Molecular Structure Preparation Ion source Acceleration (MeV) Initial quantum state? E0E0 Micro-scale Collapse Ion target effects Electron stripping Multiple scattering t=1  s to few secs t < sec 60 A thick Measurement Field free region Charge state analysis 3D imaging detector Reconstruction Macro-scale t= few  s Velocities measurement Storage ring! Z. Vager et al.

Coulomb Explosion Imaging for a Diatomic Molecular Ion

Kinetic energy release (KER) for the Coulomb Explosion Imaging of HD + after various storage time in the storage ring. Time

Distribution of the internuclear distance distribution of HD + as a function of storage time.

Vibrational population as a function of storage time Z. Amitay et al., Science, 281, 75 (1998). Solid line: fit to the data, lifetimes as free parameters

Lifetime of HD + vibrational states

Physics with vibrationally cold molecular ions Basic quantum chemistry (theory-experiment) Interesting platform for study of few particle quantum problem Molecular dynamics on single and multi-dimensional surfaces Benchmark for simple molecular systems Relevant to Plasma Physics Necessary for understanding the interstellar medium Experiments on Storage Rings: Electron induced recombination Electron induced dissociation Electron induced excitation Photon induced processes

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

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

Merged Beam Kinematics Electrons E e,m e Ions E i, m i Center of mass resolution: ~ meV resolution for zero relative kinetic energy! Electron-cold molecular ion reaction: Dissociative Recombination

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

Dissociative recombination cross section for HD + (cold) 2 sec of storage, Vibrationally relaxed P. Forck et al., 1992

Cryogenic Photocathode Driven Electron Beam. T~500 μeV

HD + + e -  H+D Advance in electron beam resolution June 2004 kT perp =500 μeV, kT par =20 μeV T rot =300 o K D. Orlov, F. Sprenger, M. Lestinski, H. Buhr, L. Lammich, A. Wolf et al. June 1992 P. Forck et al

H 2 + DR cross section for (v,J)=(0,0) H 2 + DR cross section for (v,J)=(0,1) H. Takagi, J. Phys. B, 26, 4815 (1993) Only one rotational quanta of excitation changes the whole spectra!! Recombination cross section for a single quantum rotational state of H 2 + (The simplest molecular ion!) In fact, these resonances have never been individually observed! Position Depth Shape teach everything about the dynamics taking place during the dissociation. Rotationally cold molecular ions!

Rotational temperature of fast stored beam: Probing rotational population through photodissociation. Astrophysics relevance Steady state models cannot reproduce CH + abundance. The reverse reaction is the main production process. Photodissociation through non-adiabatic coupling. Laser spectroscopy

Photodissociation Spectrum of CH + U. Hechtfischer et al, PRL, 80, 2809 (1998) T=500 o K C. Williams JCP, 85, 2699 (1986) 3 Π metastable state

Time evolution of the rotational population and comparison to a radiative model. Radiative transition (oscillator strength) can be extracted. “Easier” spectroscopy. New spectroscopic constants for CH +. U. Hechtfischer et al., PRL, 80, 2809 (1998). Asymptotic rotational temperature: T~300 (+50 -0) K. However, some new evidences shows that there are collisions (residual gas) induced processes which can internally heat the beam.

H 3 + Dissociative recombination rate coefficient: Experimental data H 3 + cannot be thermalized in a storage ring.

Calculations What happen to the rotational population when you store a hot H 3 + in a ring? Simulation of radiative rotational transitions for H 3 + starting from T rot = 0.23 eV, and calculating 245,000 transitions (J. Tennyson web-site). L. Neale, et al., Astrophys. J., 464, 516, (1996) B. M. Dinelli, et al., J. Mol. Spectr. 181, 142 (1997)

Calculations Long live states: States for which the axis of rotation is nearly parallel to the C 3v symmetry axis (K=J, K=(J-1)) Is the additional energy stored as rotational energy? J: Angular momentum K: Projection of J onto the molecular symmetry axis Simulation of radiative rotational transitions for H 3 + starting from T rot = 0.23 eV, and calculating 245,000 transitions (J. Tennyson web-site).

Production of rotationally cold H 3 + at the TSR H. Kreckel et al. (2004) Pre-trapping for Pre-cooling

TSR data (kT trans =0.5 meV) Cryring data (kT trans =2 meV) Theory (C. Green, kT trans =10 meV ) Dissociative Recombination of H 3 +

Physics with rotationally cold molecular ions: “real” interstellar conditions TSR “limits” the physics to vibrational states To achieve rotational cooling, the ring needs to be cooled to much lower temperature (~10 K) The Cryogenic Storage Ring

Ultra cold electron beam Merged neutral atomic beam

CSR and Prototype: Under design and construction at the MPIK

Physics with colder (~ 2 o K) molecular ions  Interstellar conditions  Single quantum state physics  Comparison with theoretical calculations Molecular dynamics under controlled initial conditions Dissociative recombination (single Rydberg resonance) Laser spectroscopy and transition strength Cold collisions and atom exchange State control and laser manipulation Infrared emission spectroscopy Biomolecules Cluster physics … Highly charged ions (J. Ullrich) Antiproton physics (GSI)

Molecular Ion-Neutral Exchange Reactions Merged beams The rate is usually assumed to be based on Langevin model (polarization) mechanism: σ~1/√E, where E is the collision energy Tosi et al, Phys. Rev. Lett., 67, 1254 (1991). Tosi et al, JCP, 99, 985 (1993). ~10 meV HWHM Almost no experiments (cross sections) with cold molecular ions! Model reaction: AB + + C  AC + + B

State control (state manipulation) with tunable infrared laser Extremely difficult if the initial population is made of several rotational states 300 o K situation (TSR) Boltzmann distribution ~5% ~2.5% v=0 v=1 10 o K situation (CSR) ~100% ~50% v=0 v=1 Make all previously described experiments possible with different initial quantum state!

Infrared emission spectroscopy Cerny-Turner monochromator Single Photon Cryogenic Infrared Detector (Saykally, JPC A102, 1465 (1998)) The ultimate goal: Measuring the emission lines of mass selected stored (and cooled) PAH ions and ionic clusters.