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Science 7 September 2007:
Vol. 317. no. 5843, pp. 1374 - 1378
DOI: 10.1126/science.1144920
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Reports

Soft X-ray-Driven Femtosecond Molecular Dynamics

Etienne Gagnon,1 Predrag Ranitovic,2 Xiao-Min Tong,3 C. L. Cocke,2 Margaret M. Murnane,1 Henry C. Kapteyn,1 Arvinder S. Sandhu1*

The direct observation of molecular dynamics initiated by x-rays has been hindered to date by the lack of bright femtosecond sources of short-wavelength light. We used soft x-ray beams generated by high-harmonic upconversion of a femtosecond laser to photoionize a nitrogen molecule, creating highly excited molecular cations. A strong infrared pulse was then used to probe the ultrafast electronic and nuclear dynamics as the molecule exploded. We found that substantial fragmentation occurs through an electron-shakeup process, in which a second electron is simultaneously excited during the soft x-ray photoionization process. During fragmentation, the molecular potential seen by the electron changes rapidly from nearly spherically symmetric to a two-center molecular potential. Our approach can capture in real time and with angstrom resolution the influence of ionizing radiation on a range of molecular systems, probing dynamics that are inaccessible with the use of other techniques.

1 JILA, University of Colorado, Boulder, CO 80309–0441, USA.
2 James R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, KS 66506, USA.
3 Institute of Materials Science and Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8573, Japan.

* To whom correspondence should be addressed. E-mail: arvinder{at}jila.colorado.edu; sandhu{at}physics.arizona.edu

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