Time-resolved gas electron diffraction – building a new apparatus in Edinburgh

1. Workshop on Ultrafast Electron Sources UCLA 14th December 2012 Time-resolved gas electron diffraction – building a new apparatus in Edinburgh Derek A. Wann University of Edinburgh

2. Acknowledgements Matthew Robinson Paul Lane Stuart Young Funding:

3. Overview My background • My background in solving inorganic chemistry problems using time-averaged gas-phase ED data and quantum chemical methods Apparatus development • Adapting the existing continuous source ED apparatus (not for this talk) • Designing and building a time-resolved electron diffractometer What to study? • Pump-probe studies of photoinduced dissociations / conformational changes / bond breaking or forming Future developments – including using MeV electrons in the UK

4. Electron gun CCD camera Inlet system Electron diffraction in a previous life • Performed ED studies of many novel and interesting inorganic species • Range of sizes and complexities • Understanding function using structures Dalton Trans., 2008, 96. J. Phys. Chem. A, 2007, 111, 6103. Inorg. Chem., 2011, 50, 2988. Inorg. Chem., 2012, 51, 3324.

5. Current projects • Awarded an EPSRC Career Acceleration Fellowship to do work with vibrationally cooled beams, and on time-resolved electron diffraction • Two main areas of work • developing the continuous beam apparatus • building an entirely new apparatus in Edinburgh Chemistry’s Ti:sapphire laser lab • Goals: understanding molecular structures and reaction dynamics based on direct diffraction measurements • Computational chemistry is an important part of what we do • can be very valuable in interpreting chemical phenomena

6. A 100 keV DC gun

7. New time-resolved electron diffraction • Femtosecond laser used to produce electron beam and to pump molecules • 100 keV electrons – pulsed up to kHz • space-charge repulsion • compact electron gun (simulated best resolution 500 fs) Detector chamber 100 kV electron gun chamber with vacuum pump Diffraction chamber with a magnetic lens, pulsed nozzle and vacuum pump Electron flight chamber with vacuum pump

8. Overall lab plan

9. Gases need nozzles Even-Lavie valve

10. Transition metal complexes known to undergo photoinduced isomerisations Some possible studies • Helps if species of interest has some heavy atoms and undergoes a significant structural change upon excitation • Dissociations, such as H3CS-SCH3→ H3CS·, would be very obvious • In an excited electronic state C60 has an enormous breathing mode • causes increase in diameter of 30%! • requires ~100 fs time resolution to observe S–C S–S S–C S···C C–H C–H S···H S···H C···C

11. Relativistic electrons • The EBTF at Daresburyhas a 6 MeV electron gun • Jim Clarke and colleagues keen to find uses for the apparatus • Currently simulating the beam characteristics to see if electron diffraction can be possible

12. Conclusions • Structure tells us a lot about function, but dynamics can tell us so much more • Build on expertise to perform sub-ps gas-phase ED using a compact 100 keV DC electron gun • 2013 should see the first electrons produced • Working with central laboratory to investigate performing MeV diffraction