Stockett M H, Gatchell M, Chen T, de Ruette N, Giacomozzi L, Wolf M, Schmidt H T, Zettergren H, Cederquist H
Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
J Phys Chem Lett. 2015 Nov 19;6(22):4504-9. doi: 10.1021/acs.jpclett.5b02080. Epub 2015 Nov 3.
We have measured absolute cross sections for ultrafast (femtosecond) single-carbon knockout from polycyclic aromatic hydrocarbon (PAH) cations as functions of He–PAH center-of-mass collision energy in the 10–200 eV range. Classical molecular dynamics (MD) simulations cover this range and extend up to 105 eV. The shapes of the knockout cross sections are well-described by a simple analytical expression yielding experimental and MD threshold energies of EthExp = 32.5 ± 0.4 eV and EthMD = 41.0 ± 0.3 eV, respectively. These are the first measurements of knockout threshold energies for molecules isolated in vacuo. We further deduce semiempirical (SE) and MD displacement energies, i.e., the energy transfers to the PAH molecules at the threshold energies for knockout, of TdispSE = 23.3 ± 0.3 eV and TdispMD = 27.0 ± 0.3 eV. The semiempirical results compare favorably with measured displacement energies for graphene (Tdisp = 23.6 eV).
我们测量了多环芳烃（PAH）阳离子中超快（飞秒）单碳敲除的绝对截面，该截面是质心能量在10 - 200 eV范围内的He - PAH碰撞能量的函数。经典分子动力学（MD）模拟涵盖了该能量范围，并扩展到105 eV。敲除截面的形状可以通过一个简单的解析表达式很好地描述，该表达式给出的实验和MD阈值能量分别为EthExp = 32.5 ± 0.4 eV和EthMD = 41.0 ± 0.3 eV。这些是对真空中孤立分子敲除阈值能量的首次测量。我们进一步推导了半经验（SE）和MD位移能量，即在敲除阈值能量下转移到PAH分子的能量，分别为TdispSE = 23.3 ± 0.3 eV和TdispMD = 27.0 ± 0.3 eV。半经验结果与石墨烯的测量位移能量（Tdisp = 23.6 eV）相比具有优势。
