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Advanced Instrumentation in Molecular Physics Research

This presentation by Mats Larsson delves into the cutting-edge instrumentation and experimental research in the Molecular Physics Group. Topics include electron-driven molecular processes, ultrafast chemical physics, and advanced spectroscopy techniques. Key highlights involve the production of quantum systems in defined states, detection of ionized biological molecules, and the study of vibrational excitation in gas-phase interactions. The work emphasizes collaboration between UC Berkeley and Stockholm and showcases innovative developments like the pinhole discharge source and various sophisticated mass filtering techniques.

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Advanced Instrumentation in Molecular Physics Research

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  1. Instrumentation in the Molecular Physics Group Presented by: Mats Larsson

  2. Experimental research activities • Electron-driven molecular processes • Ultrafast chemical physics • Spectroscopy of clusters • (Microwave induced chemistry) • (Linear ion trap) • (Biomedical imaging)

  3. Electron-driven molecular processes • The problem of producing quantum systems (i.e. molecules) in well defined states • How to produce ionized biological molecules in the gas phase • How to detect reaction products of electron-driven processes • How to obtain chemical information

  4. State selected molecular ions • ABC+ (, v, J) • How do we control the internal quantum states? • Excitations can be removed by storage of ABC+ in CRYRING. • This does not always work for J • This does not work for molecules of type A2+ • This does not work if we want to study ABC+ in a known distribution of excited quantum states

  5. Pinhole discharge source • Designed and built at UC Berkely • Characterized at UC Berkeley • Shipped to Stockholm for experiment at CRYRING • Shipped back to Berkeley, redesigned, and characterized • Shipped to Stockholm for new experiment

  6. Discharge Supersonic expansion including ions and neutrals High pressure Vacuum Laser beam for probing

  7. Energy level structure of H3+

  8. Interstellar transitions 2 0 ortho para

  9. Diffuse cloud absorption

  10. Control of vibrational excitation • Electron-impact source • Built and characterized at SRI International in Menlo Park, CA • Shipped AMOLF in Amsterdam and then later to Stockholm

  11. Ground Plate Deflection plates Electron Trap Extraction Plate Repeller plates Hot filament (outside the source) Gas Inlet

  12. V=0,1,2,3! V=0! Ion Source Developments • Better control over vibrational populations • Experiments on SEC and DR • More control over ion source settings • AMOLF & SRI, Phil Cosby • O2+() + Cs  O2*(Ryd,n=3,’= )  O + O + KER(0-3eV, ) • CRYRING • O2+ + e-  (O2*(Ryd) ) O2**  O + O + KER

  13. Biological molecules In the gas phase

  14. Spray needle: The needle is inside a nitrogen- gas filled housing for spray stability. Entrance capillary: The ion droplets are passing through a heated capillary and evaporate.

  15. Exit: After the capillary, the ions are stored and pulsed by a hexapole trap.

  16. Quadrople mass filter Ion trap Electrospray unit with a pulsed hexapole trap experiment Interaction of biomolecular ions with electrons/photons

  17. Beam splitter Image intensifier H CCD- camera O H MCPs and phosphor screen Timing (Camac) PC 16-segmented PMT

  18. Experimental parameters • Data taking rate: 600 - 1000 Hz • Time resolution: 0.6 - 1.0 ns • Energy resolution: 100 meV • No chemical information in the standard set-up

  19. Specifications • Data taking rate > 10 kHz • Time resolution  1 ns • Position resolution  0.1 mm • Dead area 1 cm2 • No chemical information

  20. pump (shg, thg, topas) polychromator CCD sample flow cell probe (wlc) Example: I2Br- + hn I2- + Br  I2Br-/CH3CN +

  21. The Cluster Apparatus

  22. The total cluster machine assembly, combining a laser ablation source with a time-of-flight mass spectrometer Pressure: 10-4 – 10-7 torr inside the machine The extracting electric field: static in Stark spectroscopy switched in lifetime measurements Cold molecules (Ttrans < Trot < Tvibr < Telectr )  only lowest vibrational and electronic states populated

  23. Nd:YAG laser (1064 nm) for ablation of the metal clusters • A tunable ring-dye laser, pumped by an Ar+ laser, for exciting • the molecules. • The narrow bandwidth cw laser light (FWHM ~ 1 MHz) is • pulsed-amplified in a Bethune cell, • pumped by a XeCl excimer laser (308 nm) pulses 10 ns, ~1 J, FWHM < 150 MHz • An ArF excimer laser (193 nm) for ionizing the molecules • Operating frequency: 10 Hz • Auto-scan system. Iodine calibration spectrum.

  24. Conclusions • The ion source R&D is probably too specialized to be of interest for an AlbaNova instrumentation project • The electro-optical part is covered by the KAW application • From the Molecular Physics point of view, detector development is most suited

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