Development of apparatus for x-ray absorption spectroscopy of free clusters.

我们研制了一种用于自由团簇X射线吸收光谱的新装置和一种用于自由团簇尺寸选择EXAFS测量的新方法。该装置主要由两个真空室、真空抽运系统和团体源组成。每个真空室由涡轮分子泵独立抽空，以达到产生大团簇所需的抽气速度。此外，我们还开发了一种新的团簇光源，它通过将气体或气体混合物绝热膨胀到真空室中来产生簇束。样品气体从安装在连续流动低温恒温器顶部的可互换喷嘴喷出。当低温恒温器用液氮操作时，喷嘴温度可以在77-300K之间调节，并保持恒定，精度为±1K。通过产生大的Ar团簇对装置的性能进行了评估(在典型条件下可以检测到多达20个Ar&gt；团簇)。我们建议了一个新的…利用X射线吸收后团簇去激发过程的信息对自由团簇进行尺寸选择性EXAFS测量的更多方法。为了验证我们的建议，我们已经开发了一套新的EXAFS-PEPICO同步测量数据采集系统，并于Spring-8在X射线波动束线BL10XU上对Se团束进行了EXAFS-PEPICO同步测量。虽然团簇束中Se原子的数密度比块状Se样品小十几个数量级，但用总离子产额(TiY)模式获得的X射线吸收光谱显示出明显的EXAFS振荡。对PEPICO谱峰进行积分得到的部分离子产额(Piy)谱也显示出明显的EXAFS振荡。根据尺寸选择EXAFS方法，我们推导了Se_2和Se_5团簇的EXAFS谱。“Se_5”的EXAFS振荡与Se_2的EXAFS振荡特征不同，EXAFS振荡的间距清楚地表明“Se_5”的键长大于Se_2的键长。更准确地说，前者为2.35A，后者为2.16A，这与一堆不同形式的Se的EXAFS数据完全一致。因此，我们可以得出结论，所提出的尺寸选择XAFS是一种可靠和现实的方法。较少

We have developed a new apparatus for X-ray absorption spectroscopy of free clusters and a new method for size selective EXAFS measurement of free clusters.The new apparatus mainly consists of two vacuum chambers, vacuum pumping system and cluster source. Each vacuum chamber is independently evacuated by turbo molecular pump to achieve enough pumping speed required for producing large clusters. In addition, we have developed a new cluster source which produces a cluster beam by an adiabatic expansion of gas or gas mixture into a vacuum chamber. The sample gas is ejected from the interchangeable nozzle which is mounted on top of a continuous flow cryostat. The nozzle temperature can be adjusted to values between 77 to 300 K and kept constant with an accuracy of ±1K when the cryostat is operated with liquid nitrogen. The performance of the apparatus have been evaluated by producing large argon clusters (up to Ar_<20> clusters are detected under typical condition).We have suggested a new … More method for size selective EXAFS measurement of free clusters by using the information of de-excitation process of clusters subsequent to the x-ray absorption. In order to examine our suggestion, we have developed a new data acquisition system for EXAFS-PEPICO synchronous measurement and carried out EXAFS-PEPICO synchronous measurements for Se cluster beam at the X-ray undulator beamline BL10XU in SPring-8. Although the number density of Se atoms in the cluster beam is smaller than that of bulk Se samples by more than ten orders of magnitude, the X- ray absorption spectrum which has been taken by total ion yield (TIY) mode indicates clear EXAFS oscillation. The partial ion yield (PIY) spectra which are obtained by integrating the peaks of the PEPICO spectra also show clear EXAFS oscillation. We have deduced EXAFS spectra of Se_2 and "Se_5" clusters according to the size selective EXAFS method. The EXAFS oscillation of "Se_5" differs from that of Se_2 in characteristic manner and the spacing of the EXAFS oscillation clearly demonstrates that the bond length of "Se_5" is longer than that of Se_2. More precisely, the former proves to be 2.35A and the latter 2.16A, which is fully consistent with a pile of EXAFS data for various forms of Se. Therefore, we may conclude that the proposed size-selective XAFS is a reliable and realistic method. Less