Université de Bordeaux - CNRS - CEA, CELIA, UMR5107, F33405 Talence, France.
Synchrotron SOLEIL, Saint Aubin, BP 34, 91192 Gif-sur-Yvette, France.
Faraday Discuss. 2016 Dec 16;194:325-348. doi: 10.1039/c6fd00113k.
Measuring the ultrafast dynamics of chiral molecules in the gas phase has been a long standing and challenging quest of molecular physics. The main limitation to reach that goal has been the lack of highly sensitive chiroptical measurement. By enabling chiral discrimination with up to several 10% of sensitivity, photoelectron circular dichroism (PECD) offers a solution to this issue. However, tracking ultrafast processes requires measuring PECD with ultrashort light pulses. Here we compare the PECD obtained with different light sources, from the extreme ultraviolet to the mid-infrared range, leading to different ionization regimes: single-photon, resonance-enhanced multiphoton, above-threshold and tunnel ionization. We use single and multiphoton ionization to probe the ultrafast relaxation of fenchone molecules photoexcited in their first Rydberg states. We show that time-resolved PECD enables revealing dynamics much faster than the population decay of the Rydberg states, demonstrating the high sensitivity of this technique to vibronic relaxation.
测量气相中手性分子的超快动力学一直是分子物理学中的一个长期而具有挑战性的课题。实现这一目标的主要限制因素一直是缺乏高灵敏度的手性测量。通过实现高达百分之几的灵敏度的手性区分，光电离圆二色性（PECD）为解决这个问题提供了一种方法。然而，跟踪超快过程需要用超短光脉冲测量 PECD。在这里，我们比较了从极紫外到中红外范围的不同光源获得的 PECD，导致不同的电离状态：单光子、共振增强多光子、阈上和隧道电离。我们使用单光子和多光子电离来探测在其第一里德伯态中光激发的迷迭香酮分子的超快弛豫。我们表明，时间分辨的 PECD 能够揭示比里德伯态的衰减快得多的动力学，证明了该技术对振动态弛豫的高灵敏度。
