J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA.
Phys Rev Lett. 2015 Mar 20;114(11):113001. doi: 10.1103/PhysRevLett.114.113001. Epub 2015 Mar 16.
A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200 meV) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei.
从激光驱动的高次谐波中选择具有高光谱分辨率（<200 毫电子伏特）的飞秒真空紫外（VUV）脉冲。这个超快的 VUV 脉冲与红外（IR）激光脉冲同步，以研究氘分子中的离解电离。在 VUV 光子能量为 16.95 eV 时，发现了一种以前未观察到的键断裂途径，其中解离方向不遵循 IR 偏振。我们将其解释为对应于分子预离解成两个分离的原子，其中一个原子被随后的 IR 脉冲光致电离。时间分辨研究允许我们确定中间预离解过程的寿命约为 1 ps。此外，离解电离途径对 VUV 光子能量非常敏感。随着 VUV 光子能量蓝移到 17.45 eV，更熟悉的键软化通道被打开以与新发现的途径竞争。电子和核之间的能量共享支持不同途径的解释。
