基于极紫外自由电子激光的中性团簇红外光谱

团簇在能源催化和大气雾霾等诸多化学过程中广泛存在，团簇表征与性能研究对诠释化学反应机理至关重要. 然而，中性团簇由于缺乏电荷、难于探测，实验研究非常困难. 鉴于上述情况，发展了基于极紫外自由电子激光的中性团簇红外光谱实验方法，用于质量选择中性团簇的高灵敏探测、结构表征和性能研究. 红外-极紫外衰减和红外+极紫外增强光谱实验方法已被应用于一些中性水团簇和一些中性金属羰基化合物的研究. 由于极紫外自由电子激光的波长范围涵盖了绝大多数中性团簇的第一电离势，这一独特的实验方法为开展各类中性团簇红外谱学和结构的研究打开了大门. 本文综述了这些红外光谱实验方法及其在中性团簇研究中的应用.

Infrared Spectroscopy of Neutral Clusters Based on a Vacuum Ultraviolet Free Electron Lase

Spectroscopic characterization of clusters is crucial to understand-ing the structures and reaction mechanisms at the microscopic level, but it has been proven to be a grand challenge for neutral clusters because the absence of a charge makes it difficult for the size selection and detection. In-frared (IR) spectroscopy based on threshold photoionization using a tunable vacuum ultraviolet free electron laser (VUV-FEL) has recently been developed in the lab. The IR-VUV depletion and IR+VUV enhancement spectroscopic techniques open new avenues for size-selected IR spectroscopies of a large va- riety of neutral clusters without con nement (i.e., an ultraviolet chromophore, a messenger tag, or a host matrix). The spectroscopic principles have been demonstrated by investi-gations of some neutral water clusters and some metal carbonyls. Here, the spectroscopic principles and their applications for neutral clusters are reviewed.