Instrumentation in the Molecular Physics Group

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Instrumentation in the Molecular Physics Group

• Presented by
• Mats Larsson

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Experimental research activities

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

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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

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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

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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

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Discharge
Supersonic expansion including ions and neutrals
High pressure
Vacuum
Laser beam for probing
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Energy level structure of H3
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Interstellar transitions
?2
0
ortho para
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Diffuse cloud absorption
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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

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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,n3,? ?) ? O O
  KER(0-3eV, ?)
• CRYRING
• O2 e- ? (O2(Ryd) ?) O2 ? O O KER

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Biological molecules

• In the gas phase

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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.
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Exit After the capillary, the ions are stored
and pulsed by a hexapole trap.
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experiment
Interaction of biomolecular ions with
electrons/photons
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Beam splitter
Image intensifier
H
CCD- camera
O
H
MCPs and phosphor screen
Timing (Camac)
PC
16-segmented PMT
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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

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Specifications

• Data taking rate gt 10 kHz
• Time resolution ? 1 ns
• Position resolution ? 0.1 mm
• Dead area 1 cm2
• No chemical information

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Example
I2Br- hn ? I2- Br
?
I2Br-/CH3CN

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The Cluster Apparatus
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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 lt
Trot lt Tvibr lt Telectr ) ? only lowest
vibrational and electronic states populated
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• NdYAG 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 lt 150 MHz
• An ArF excimer laser (193 nm) for ionizing the
  molecules
• Operating frequency 10 Hz
• Auto-scan system. Iodine calibration spectrum.

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Conclusions

• The ion source RD 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