Illuminating Molecules From Within


Using COLTRIMS momentum-imaging techniques to study photodissociation of
simple molecules gives extraordinarily detailed results, allowing
examination of the molecules almost as if they were "illuminated from within".

 

 
One atom of the molecule is ionized just above the K edge and the photoelectron angular distribution is measured for a fixed orientation of the molecule. Shown here is the schematic for CO.
 

 
The molecule is fixed in space by detecting the fragments from dissociation of the molecule in coincidence with the photoelectron.
 

 
The angular distributions of the photoelectrons can be interpreted as if they were
the result of a two-slit diffraction experiment. Shown are angular distributions
of photoelectrons from K ionization in CO.

[U. Becker, X99 Proceedings, p.205 (AIP 506, 1999)]

This data may be viewed as an AVI-style video (4.1 MB in size).
Note that these videos are best viewed on a large, high-resolution display.

 

 
These are momentum images of photoelectrons ejected from the C K-shell in CO.

The molecule, the polarization vector, the incoming photon propagation vector and the photoelectron are all restricted to lie in the plane of the page in this view. The X ray energy, and thus the photoelectron energy, was scanned.

[Landers, et al, PRL 87,013002(2001)]

This data is also viewable as an AVI-style video (760 kB in size).

 

 
Both theoretical and experimental results for the dependence on KER in CO are shown here.

For long lived molecular states the dissociation is so slow that the photoelectron correlation is washed out.

[Experiment: Th. Weber et al, JPB 34, 3669 (2001)]

[Theory: R.Diez Muino, et al, J.Electron Spec.Relat.Phenom. 99,114(2001)]

 

 
The photoelectron angular distribution just above the K edge in nitrogen, showing the nice f-wave shape resonance structure.

This plot may also be viewed as an AVI-style video (1.3 MB in size).

 

 
The off-resonance, 295 eV structure, on the left, compared to the f-wave shape
resonance at 302 eV on the right, in ethylene (C2H4).

Both the off-resonance and on-resonance plots can be viewed as AVI-style videos
(about 1.5 MB each in size) by clicking either the links or the images above.

 

 
This work is the fruit of large and widespread collaboration:
At Kansas State University:
C. Lewis Cocke, Timur Osipov, Imad Ali

At the University of Frankfurt:

Reinhard Dörner, Horst Schmidt-Böcking, Thorsten Weber, Alexandra Knapp, Till Jahnke, Lothar Schmidt, Sven Schössler, Harald Bräuning, Achim Czasch

At Western Michigan University:

Allen Landers

At the Lawrence-Berkeley National Lab:

Michael H. Prior, Jürgen Rösch, Andre Staudte

and at GANIL/CIRIL:

Amine Cassimi
 

 

This page was distilled from PowerPoint presentations.
Lew Cocke (KSU) presented at the DOE AMO Workshop at Granlibakken;
his complete presentation is available as an 8 MB zip archive.
Allen Landers (Western Michigan) gave his talk at ICPEAC 2001 in Santa Fe;
it is available as a 7.4 MB zip archive.

Previous work on this subject is highlighted in web pages from 1999 and 2000.
Further information on this research is available from Professor Lew Cocke.