- Pulsed supersonic jet
- Electron gun
- Molecular beam skimmer
- Extraction and acceleration of negative ion to a nominal energy
- Re-referencing, gating, and bunching of ion-packet
2m Time-of-flight mass separation stage
- & 8. Electrostatic ion beam deflectors
- four unipotential, or Einzel lenses
- beam apertures
- Potential re-referencing switch, beam deflectors & potential barrier: in combination with the ion gating, bunching, and potential re-referencing unit, mass resolving powers of m/Δm = 350-400 are achieved .
- Velocity-map imaging system - based on Eppink and Parker design , but modified and placed on an on-axis orientation (ΔE/E ~ 0.2-0.3 %
- (hν) 2nd harmonic (532nm) of Nd:YAG laser, Continuum Powerlite 9010
- matched pair of 75mm high spatial resolution micro-channel plates (MCPs) coupled to a phosphor detector
- high resolution CCD camera (1600 x 1200 pixels) centroided to 4800 x 3600 pixels, data analysis dome using a modified Abel inversion method [3a, 3b]
|Ion beam energy:||500-535 eV|
|Ion beam divergence:||~ 1-2x103 rad|
|Ion beam size:||2.0 mm3|
|Laser beam wavelength:||532 nm|
|Laser beam size:||2 mm diameter|
|Interaction region size:||2 mm3|
- Raw, unprocessed, photoelectron image (4800x3600 pixels)
- Inverse Abel transformed image
- A 10o slice through the raw PE image (horizontal and vertical)
- Integrated total PE intensity taken from transformed image
The spectrum (circles) is well represented by Gaussian functions (lines)
Chemical reaction dynamics
For some molecular species only the negative ion exists, with the neutral breaking apart if the negative charge is lost. The corresponding neutral species may represent an intermediate state of a chemical reaction (ABC), A + BC ↔ ABC ↔ AB + C, that is present for a short period of time, called a transition state. The transition state controls the rate of a reaction and is very difficult to study due to its short lifetime during the course of a chemical reaction. The photodetachment process provides a method to access the transition state directly
Photodetachment may yield a radical which is energetically unstable, that breaks apart. The spectra reveal details of the anion an neutral reaction path potential surfaces
References D. W. Chandler and P. L. Houston, Journal of Chemical Physics 87, 1445-1447 (1987).
 A. T. J. B. Eppink and D. H. Parker, Review of Scientific Instruments 68, 3477-3484 (1997).
 S. J. Cavanagh, S. T. Gibson, M. N. Gale, C. J. Dedman, E. H. Roberts, and B. R. Lewis, Physical Review A, submitted (July 2007).
 C. J. Dedman, E. H. Roberts, S. T. Gibson, and B. R. Lewis, Review of Scientific Instruments 72, 2915-2922 (2001).
 Research highlight (PDF 441k), RSPhysSE Annual Report (2003).