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Originally published in Science Express on 30 October 2008
Science 21 November 2008:
Vol. 322. no. 5905, pp. 1207 - 1211
DOI: 10.1126/science.1163077
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Research Articles

Time-Resolved Dynamics in N2O4 Probed Using High Harmonic Generation

Wen Li,1* Xibin Zhou,1 Robynne Lock,1 Serguei Patchkovskii,2 Albert Stolow,2 Henry C. Kapteyn,1 Margaret M. Murnane1

The attosecond time-scale electron-recollision process that underlies high harmonic generation has uncovered extremely rapid electronic dynamics in atoms and diatomics. We showed that high harmonic generation can reveal coupled electronic and nuclear dynamics in polyatomic molecules. By exciting large amplitude vibrations in dinitrogen tetraoxide, we showed that tunnel ionization accesses the ground state of the ion at the outer turning point of the vibration but populates the first excited state at the inner turning point. This state-switching mechanism is manifested as bursts of high harmonic light that is emitted mostly at the outer turning point. Theoretical calculations attribute the large modulation to suppressed emission from the first excited state of the ion. More broadly, these results show that high harmonic generation and strong-field ionization in polyatomic molecules undergoing bonding or configurational changes involve the participation of multiple molecular orbitals.

1 JILA and Department of Physics, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309–0440, USA.
2 Steacie Institute for Molecular Sciences, National Research Council, Ottawa, ON K1A 0R6, Canada.

* To whom correspondence should be addressed. E-mail: wli{at}jila.colorado.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)