J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, 66503, USA.
Phys Rev Lett. 2011 Aug 5;107(6):063201. doi: 10.1103/PhysRevLett.107.063201. Epub 2011 Aug 2.
The process by which a molecule in an intense laser field ionizes more efficiently as its bond length increases towards a critical distance R(c) is known as charge resonance enhanced ionization (CREI). We make a series of measurements of this process for CO(2), by varying pulse duration from 7 to 200 fs, in order to identify the charge states and time scales involved. We find that for the 4+ and higher charge states, 100 fs is the time scale required to reach the critical geometry <R(CO)> ≈ 2.1 Å and <θ(OCO)> ≈ 163° (equilibrium CO(2) geometry is <R(CO)> ≈ 1.16 Å and <θ(OCO)> ≈ 172°). The CO(2)(3+) molecule, however, appears always to begin dissociation from closer than 1.7 Å indicating that dynamics on charge states lower than 3+ is not sufficient to initiate CREI. Finally, we make quantum ab initio calculations of ionization rates for CO(2) and identify the electronic states responsible for CREI.
在强激光场中，分子的键长增加到临界距离 R(c)时，其离化效率会更高，这种过程被称为电荷共振增强离化（CREI）。我们通过改变脉冲持续时间从 7 到 200 fs，对 CO(2) 中的这个过程进行了一系列测量，以确定涉及的电荷状态和时间尺度。我们发现，对于 4+和更高的电荷状态，达到临界几何形状<R(CO)>≈2.1 Å 和<θ(OCO)>≈163°（平衡 CO(2) 几何形状为<R(CO)>≈1.16 Å 和<θ(OCO)>≈172°）需要 100 fs 的时间尺度。然而，CO(2)(3+)分子似乎总是从小于 1.7 Å 的距离开始离解，这表明电荷状态低于 3+的动力学不足以引发 CREI。最后，我们对 CO(2) 的离化率进行了量子从头计算，并确定了引发 CREI 的电子态。
