1. Photoelectron Velocity Map Imaging of Vibrationally Excited, Gas-phase Biomolecules and their Anions
Daniël Bakker, Sjors Bakels, Rutger van der Made, Atze Peters, Anouk Rijs FELIX Laboratory Radboud University Nijmegen, the Netherlands

2. Molecular and Biophysics Group @ FELIX Laboratory
In our group, at RU, exploit far-IR or THZ radiation to study H-bonds, biomolecules, while focussing on the behavior of peptides.
To remain state-of-the-art, there is of course always some instrumental debelopment work
Today focus on this , but indirectly only on these 2
Far-IR and THz
spectroscopy

3. IR Spectroscopy for ALL Structural Information
Structural characterization
ground state
Structural characterization
without chromophore
Structural characterization
excited state
Problem: How to observe IR absorption?
Ik denk dat dit meer past bij de intro en wat we in de groep doen! UV
UV’
VUV IR UV UV IR IR
Conformer selective IR
IR-VUV spectroscopy
UV-IR-UV spectroscopy

4. Excess energy shows absorption
Excess energy, and thus kinetic energy Ekin of electrons different!
 Use velocity map imaging to measure Ekin of electrons
Particles leave interaction region in spherical shell
 Newton sphere
Whole sphere is accelerated towards position-sensitive detector
MCP, phosphor screen and camera
Eexc
Eexc
UV’
UV’ IR UV

5. Setup Skimmed supersonic expansion of neutrals
desorption laser
skimmer
Skimmed supersonic expansion of neutrals
heatable sample container
laser desorption
Interaction with IR and UV light in between HV plates
Ions can be steered upwards for TOF analysis
Ions or electrons can be accelerated downward for VMI
valve
Sample bar
molecular beam

6. Calibration for electron imaging: Photoionization of Nitric Oxide (NO)
Resonance Enhanced Multi Photon Excitation (REMPI) spectrum of NO shows several vibrational progressions
Photoelectron spectrum shows a single large peak at 1.69 eV
 energy per pixel calibration possible
 Low energy electrons visible
Raw
Abel inverse
Miller et al. J. Chem. Phys., 1981, 75,

7. Calibration for ion imaging: Oxygen dissociation
UV spectrum shows several rotational progressions
Using largest UV peak, oxygen dissociation observed
Resolution of our experiment is as expected
Raw
Abel inverse
Groot banden plaatje Farooq thesis als illustratie van rijkheid aan ringen

8. Phenol Ion and Electron Spectroscopy
Ions
Electrons

9. Phenol Fragmentation Patterns
m = 39, C3H3+
Phenol Fragmentation Patterns
Lens was used to create small interaction region
Multiple fragmentation pathways of phenol observed
Using gating: images of different, isolated fragments
m = 65, C5H5+
m = 94, C6H5OH+
m = 66, C5H6+

10. Experimental Outlook: Electronically Excited States of Xanthone
Excited state crosses over to long-lived triplet state
Long lifetime of triplet state enables illumination by long FELIX pulses
Results observed by Gerhards et al.
Contrast between on threshold and over threshold ionization
Photoelectrons provide contrast even if ions will not
Eexc
Eexc D0
IR+UV’
REMPI spectrum Xanthone as measured using LD in our lab?
UV’
ISC Sn Tn UV S0
Bartl et al. ChemPhysChem, 2009, 10, 1882 – 1886
Collaboration with Prof. W.J. Buma, University of Amsterdam

11. Conclusions
Velocity Map Imaging successfully implemented in our setup
First experiments show promising results
Adequate energy resolution
Ion fragmentation experiments
Experiments planned to use VMI on large molecules together with FELIX
Excited state spectroscopy
VUV spectroscopy
UV’ IR UV

12. Acknowledgements Anouk Rijs Sjors Bakels Atze Peters
Rutger van der Made
Molecular and Biophysics group FELIX team & Technical support