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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
Author NameAffiliationE-mail
Zhou Lu Department of Chemistry, University of California, Davis CA 95616, USA  
Hong Gao Department of Chemistry, University of California, Davis CA 95616, USA  
Yun-tao Xu Department of Chemistry, University of California, Davis CA 95616, USA  
Lei Yang Department of Chemistry, University of California, Davis CA 95616, USA  
Chow-Shing Lam Department of Chemistry, University of California, Davis CA 95616, USA  
Yanice Benitez Department of Chemistry, University of California, Davis CA 95616, USA  
C. Y. Ng Department of Chemistry, University of California, Davis CA 95616, USA cyng@ucdavis.edu 
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
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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