Gas phase spectroscopy at the CLS

VLS-PGM Beamline Y Hu et al, Rev. Sci. Instrum. 78 (2007) p083109

VLS-PGM Beamline

Instruments for gas-phase science at the VLS-PGM beamline Dual toroidal electrostatic analyser Wiley-McLaren time-of-flight mass spectrometer

Dual toroidal analyser T J Reddish et al (1997) Rev. Sci. Instrum A E Slattery et al (2000) J. Phys. B Toroidal analysers can energy select the charged particles (ions/ electrons) while preserving the initial angle of emission. Both analysers are independent and each can be switched to detect electrons or ions. Both can operate in threshold (TPES) mode Detectors can operate in coincidence mode

Dual toroidal analyser

Since the toroidal analyser preserves the azimuthal angle of emission of the photoelectron we can find the photoelectron asymmetry parameter across a photoelectron spectrum. That is we can record “beta paramer” spectra. The spectra here are beta parameter spectra for H 2 and will be the subject of the 2 nd half of this talk. Finally we remember that the detectors can be configured for electrons or ions.

Time of Flight Electron Start – Ion Stop, with multi-hit electronics No energy discrimination on the electron Allows ToF mass spectra and PePIPICO 2D maps

Time of Flight Parent “C 4 ” “C 3 ” “C 2 ” Water “C 1 ”

ToF PePIPICO para-nitroaniline

Time of Flight

If any of this would be of interest to you please talk to me at this symposium. Michael MacDonald Canadian Light Source Inc. 44 Innovation Boulevard Saskatoon, SK, S7N 2V

Hydrogen

Direct mechanisms (a) and (b) produce only a limited range of electron energies due to Franck-Condon Factor restrictions Indirect mechanisms (c) and (d) produce a wide range of electron kinetic energies. Further mechanism (d) can decay to either the bound σ g or dissociative σ u state of the ion. Remember in quantum mechanics indistinguishable paths to the same destination interfere.

Hydrogen

Red – experimental results Black – full QM closed coupling calculations

Hydrogen

Results and the simplified model

Summary of H 2 results Unusual properties of observed interference Interference shows in direction of photoelectrons not intensity Direction of photoelectrons are dictated by nuclear motion (Ultimately it all comes back to symmetry !) Interference is from different autoionisation paths from a coherent superposition of electronic states. (Not direct ionisation and autoionisation from a single excited state) This is not a coincidence experiment, and, indeed, the oscillations would disappear in a coincidence experiment.

Acknowledgements Dr. Tim Reddish Dr. Arathi Padmanabhan Dr. Smialek-Telega Prof. Nigel Mason Dr. Lucia Zuin Ru Igarishi Antonio C.O. Guerra and Cássia C. Turci Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ , Brazil Dr. J. Fernández Dr. A. Palacios Prof. F. Martín