Bond-length dependence of attosecond ionization delays in O <sub>2</sub> arising from electron correlation to a shape resonance
Daniel Hammerland, Thomas Berglitsch, Pengju Zhang, Tran Trung Luu, Kiyoshi Ueda, Robert R. Lucchese, Hans Jakob Wörner
Abstract
We experimentally and theoretically demonstrate that electron correlation can cause the bond-length sensitivity of a shape resonance to induce an unexpected vibrational state–dependent ionization delay in a nonresonant channel. This discovery was enabled by a high-resolution attosecond-interferometry experiment based on a 400-nm driving and dressing wavelength. The short-wavelength driver results in a 6.2–electron volt separation between harmonics, markedly reducing the spectral overlap in the measured interferogram. We demonstrate the promise of this method on O 2 , a system characterized by broad vibrational progressions and a dense photoelectron spectrum. We measure a 40-attosecond variation of the photoionization delays over the X 2 Π g vibrational progression. Multichannel calculations show that this variation originates from a strong bond-length dependence of the energetic position of a shape resonance in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi mathvariant="normal">b</mml:mi> <mml:mn>4</mml:mn> </mml:msup> <mml:msubsup> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mi>g</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> channel, which translates to the observed effects through electron correlation. The unprecedented energy resolution and delay accuracies demonstrate the promise of visible-light–driven molecular attosecond interferometry.