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Science 14 November 2008:
Vol. 322. no. 5904, pp. 1081 - 1085
DOI: 10.1126/science.1164498
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Reports

Observing the Creation of Electronic Feshbach Resonances in Soft X-ray–Induced O2 Dissociation

Arvinder S. Sandhu,1*{dagger} Etienne Gagnon,1* Robin Santra,2,3 Vandana Sharma,1 Wen Li,1 Phay Ho,2 Predrag Ranitovic,4 C. Lewis Cocke,4 Margaret M. Murnane,1{ddagger} Henry C. Kapteyn1

When an atom or molecule is ionized by an x-ray, highly excited states can be created that then decay, or autoionize, by ejecting a second electron from the ion. We found that autoionization after soft x-ray photoionization of molecular oxygen follows a complex multistep process. By interrupting the autoionization process with a short laser pulse, we showed that autoionization cannot occur until the internuclear separation of the fragments is greater than approximately 30 angstroms. As the ion and excited neutral atom separated, we directly observed the transformation of electronically bound states of the molecular ion into Feshbach resonances of the neutral oxygen atom that are characterized by both positive and negative binding energies. States with negative binding energies have not previously been predicted or observed in neutral atoms.

1 JILA, University of Colorado at Boulder, Boulder, CO 80309, USA.
2 Argonne National Laboratory, Argonne, IL 60439, USA.
3 Department of Physics, University of Chicago, Chicago, IL 60637, USA.
4 J. R. MacDonald Lab, Department of Physics, Kansas State University, Manhattan, KS 66506, USA.

* These authors contributed equally to this work.

{dagger} Present address: Department of Physics, University of Arizona, Tucson, AZ 85721–0081, USA.

{ddagger} To whom correspondence should be addressed. E-mail: margaret.murnane{at}colorado.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Phase matching of high harmonic generation in the soft and hard X-ray regions of the spectrum.
T. Popmintchev, M.-C. Chen, A. Bahabad, M. Gerrity, P. Sidorenko, O. Cohen, I. P. Christov, M. M. Murnane, and H. C. Kapteyn (2009)
PNAS 106, 10516-10521
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