Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany.
J Phys Chem A. 2013 May 30;117(21):4394-403. doi: 10.1021/jp401424w. Epub 2013 May 14.
Helium nanodroplets are widely used as a cold, weakly interacting matrix for spectroscopy of embedded species. In this work, we excite or ionize doped He droplets using synchrotron radiation and study the effect onto the dopant atoms depending on their location inside the droplets (rare gases) or outside at the droplet surface (alkali metals). Using photoelectron-photoion coincidence imaging spectroscopy at variable photon energies (20-25 eV), we compare the rates of charge-transfer to Penning ionization of the dopants in the two cases. The surprising finding is that alkali metals, in contrast to the rare gases, are efficiently Penning ionized upon excitation of the (n = 2)-bands of the host droplets. This indicates rapid migration of the excitation to the droplet surface, followed by relaxation, and eventually energy transfer to the alkali dopants.
氦纳米液滴被广泛用作嵌入物种光谱学的冷、弱相互作用基质。在这项工作中，我们使用同步辐射激发或离化掺杂的氦液滴，并研究其对掺杂原子的影响，具体取决于它们在液滴内部（稀有气体）或液滴表面（碱金属）的位置。通过在可变光子能量（20-25 eV）下进行光电子-光电离符合成像光谱学研究，我们比较了两种情况下掺杂剂的电荷转移到彭宁离化的速率。令人惊讶的发现是，与稀有气体相比，当激发主体液滴的（n = 2）带时，碱金属可以有效地通过彭宁离化。这表明激发迅速迁移到液滴表面，然后是弛豫，最终能量转移到碱金属掺杂剂。
