Institute of Chemistry, Chinese Academy of Science, Beijing 100190, People's Republic of China.
J Phys Chem A. 2010 Mar 11;114(9):3087-95. doi: 10.1021/jp907662z.
Superexcited states (SESs) of oxygen molecules and their neutral dissociation processes have been studied both experimentally and theoretically using intense femtosecond laser. We find that at the laser intensity of approximately 2 x 10(14) W/cm(2), ultrashort laser pulse causes neutral dissociation of oxygen molecule by way of SESs. The dissociation products are the excited neutral oxygen atoms, which are observed through fluorescence spectroscopy. Laser power dependence of the fluorescence intensity shows that each molecule effectively absorbs an average of ten laser photons. The total energy absorbed is sufficient to stimulate the molecule to many of the SESs. The effect is equivalent to single photon excitation in the extreme-ultraviolet (XUV) region by synchrotron radiation (SR). Morse potential energy curves (PECs) are constructed for the SESs of O(2) molecules. In light of the PECs, predissociation mechanism is proposed for the neutral dissociation. Quasi-classical trajectory (QCT) calculations show that the predissociation time is as short as 100 fs, which is consistent with our experimental measurement using ultrafast pump-probe technique.
使用高强度飞秒激光，从实验和理论两方面研究了氧分子的超激发态（SESs）及其中性离解过程。我们发现，在大约 2×10^14 W/cm^2 的激光强度下，超短激光脉冲通过 SESs 导致氧分子中性离解。离解产物是激发态中性氧原子，通过荧光光谱观察到。荧光强度的激光功率依赖性表明，每个分子有效地吸收了大约十个激光光子。吸收的总能量足以将分子激发到许多 SESs 中。这种效果相当于同步辐射（SR）在极紫外（XUV）区域的单光子激发。为 O(2)分子的 SESs 构建了 Morse 势能曲线（PECs）。根据 PECs，提出了中性离解的预离解机制。准经典轨迹（QCT）计算表明，预离解时间短至 100 fs，与我们使用超快泵浦探测技术进行的实验测量一致。
