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High-Resolution Threshold Photoelectron Spectroscopy by Vacuum Ultraviolet Laser Velocity-Map-Imaging Method
Zhou Lu, Hong Gao, Yun-tao Xu, Lei Yang, Chow-Shing Lam, Yanice Benitez, C. Y. Ng
Department of Chemistry, University of California, Davis CA 95616, USA
Abstract:
We have obtained the high-resolution threshold photoelectron (TPE) spectra of chlorobenzene C6H5Cl (X1A1), propargyl radical C3H3 (X2B1), and allyl radical C3H5 (X2A1) by employing the vacuum ultraviolet (VUV) laser velocity-map-imaging-TPE (VUV-VMI-TPE) method. The photoelectron energy resolution of 1-2 cm-1 observed for the VUV-VMI-TPE method is comparable to that achieved in VUV laser pulsed-field ionization-photoelectron (VUV-PFI-PE) measurements. Similar to VUV-PFI-PE measurements, the energy resolutions for VUV-VMI-photoelectron (VUV-VMI-PE) and VUV-VMI-TPE measurements are found to depend on the dc electric field F in V/cm used at the photoionization region for electron extraction. The decrease of the ionization thresholds of C6H5Cl and C3H3 observed as a function of F shows that the Stark shift correction for VUV-VMI-TPE measurements is governed by the formula -3.1√F in cm-1, which is half of the classical prediction of -6.1√F in cm-1.} We have also measured the VUV-VMI-PE spectra of C6H5Cl and C3H5 at VUV energies near their ionization thresholds. The cationic vibrational bands observed in the VUV-VMI-PE measurements were assigned to be the vibrational progression, nv7+ (n=0-3), for C3H5+. The higher experimental sensitivity and similar energy resolutions achieved in VUV-VMI-TPE compared to VUV-PFI-PE measurements make the VUV-VMI-TPE method an excellent alternative for high-resolution VUV-PFI-PE measurements.
Key words:  Photoionization  Threshold photoelectron  Velocity-map imaging  Radical
FundProject:
高分辨率初始光电子能谱由真空紫外激光速度——映射图像的方法
律洲, 高蕻, 徐运涛, 杨磊, 林周成, YaniceBenitez, 伍灼耀
加州大学戴维斯分校化学系, 戴维斯 95616
摘要:
通过采用真空紫外(VUV)激光速度-地图成像-TPE(真空紫外VMI-TPE)方法获得了高分辨率初始光电子(TPE)氯苯(C6H5Cl(X1A1))的光谱,炔丙基自由基(C3H3(X2B1))和烯丙基(C3H5(X2A1)). 观察到的真空紫外VMI-TPE方法的光电子能量分辨率在1~2 cm-1,可以和在真空紫外激光脉冲场电离光电子(VUV-PFI-PE)的测量媲美. 类似真空紫外PFI-PE测量,真空紫外VMI-光电子(真空紫外VMI-PE)和真空紫外VMI-TPE测量能量分辨率依赖于直流电场在光电离区加速电子. C6H5Cl和C3H3的电离初始值的降低为F的函数表示Stark偏移校正为VUV-VMI-TPE测量由-3.1√F管辖,这是半经典预测值-6.1√F的一半. 我们还测量C6H5Cl和C3H5的真空紫外光能量的真空紫外VMI-PE谱接近其电离初始值. 在VUV-VMI-PE测量中观察到的C3H5+阳离子振动谱和振动级数,nv7+(n=0~3). 真空紫外VMI-TPE可以实现更高的实验灵敏度和类似真空紫外PFI-PE测量的能量分辨率,使真空紫外VMI-TPE法成为高分辨率真空紫外PFI-PE测量一个很好的替代.
关键词:  光电离  初始光电子  速度-地图成像  自由基
DOI:10.1063/1674-0068/29/cjcp1512247
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