Sandhu Arvinder S, Gagnon Etienne, Santra Robin, Sharma Vandana, Li Wen, Ho Phay, Ranitovic Predrag, Cocke C Lewis, Murnane Margaret M, Kapteyn Henry C
JILA, University of Colorado at Boulder, Boulder, CO 80309, USA.
Science. 2008 Nov 14;322(5904):1081-5. doi: 10.1126/science.1164498.
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.
当一个原子或分子被X射线电离时，会产生高度激发态，然后通过从离子中射出第二个电子而衰变或自电离。我们发现，分子氧在软X射线光电离后的自电离遵循一个复杂的多步过程。通过用短激光脉冲中断自电离过程，我们表明，直到碎片的核间距大于约30埃时，自电离才会发生。随着离子和激发的中性原子分离，我们直接观察到分子离子的电子束缚态转变为中性氧原子的费什巴赫共振，其特征是具有正结合能和负结合能。以前在中性原子中尚未预测或观察到具有负结合能的态。
