分子束多原子分子之紫外光光電子影像

Vacuum ultraviolet photoelectron imaging of polyatomic molecules in supersonic molecular beams

廖雪兒(Suet-Yi Liu)

指導教授 ： 李遠鵬 ； 鈴木俊法

國立交通大學/理學院/應用化學系所/博士(2011年)

https://doi.org/10.6842/NCTU.2011.00052

摘要

I have constructed a He(I) ultraviolet photoelectron spectrometer using a supersonic molecular beam and a two-dimensional position-sensitive detector of photoelectrons. The photoelectron imaging (PEI) spectrometer enabled measurements of photoelectron spectra and photoelectron angular distributions with an efficiency considerably higher than a conventional spectrometer using a hemispherical energy analyzer. The most crucial factor for this achievement was to overcome high susceptibility of PEI to background electrons generated by scattered He(I) radiation. I examined various designs of electrodes experimentally and computationally and identified the main source of the background photoemission as the repeller plate used for acceleration of electrons. I designed a new electrostatic lens that intercepts background photoelectrons from the repeller plate traveling toward the imaging detector. High energy resolution (E/E) of 0.735 % was achieved at E = 5.461 eV with He(I) radiation that has rather poor beam characteristics. The photoelectron angular anisotropies as a function of photoelectron kinetic energies are presented for jet-cooled benzene and pyridine.
The PEI spectrometer was also employed in photoionization experiments using a vacuum ultraviolet free electron laser (VUV-FEL) at SPring-8 in Japan as a light source. A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser as a pump pulse and the VUV-FEL as a probe pulse is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed. The VUV radiation allowed us to observe the entire Franck-Condon envelope in photoionization from a transient electronic state, which was not possible in UV-DUV experiment in the laboratory.

關鍵字

電子影像

並列摘要

I have constructed a He(I) ultraviolet photoelectron spectrometer using a supersonic molecular beam and a two-dimensional position-sensitive detector of photoelectrons. The photoelectron imaging (PEI) spectrometer enabled measurements of photoelectron spectra and photoelectron angular distributions with an efficiency considerably higher than a conventional spectrometer using a hemispherical energy analyzer. The most crucial factor for this achievement was to overcome high susceptibility of PEI to background electrons generated by scattered He(I) radiation. I examined various designs of electrodes experimentally and computationally and identified the main source of the background photoemission as the repeller plate used for acceleration of electrons. I designed a new electrostatic lens that intercepts background photoelectrons from the repeller plate traveling toward the imaging detector. High energy resolution (E/E) of 0.735 % was achieved at E = 5.461 eV with He(I) radiation that has rather poor beam characteristics. The photoelectron angular anisotropies as a function of photoelectron kinetic energies are presented for jet-cooled benzene and pyridine.
The PEI spectrometer was also employed in photoionization experiments using a vacuum ultraviolet free electron laser (VUV-FEL) at SPring-8 in Japan as a light source. A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser as a pump pulse and the VUV-FEL as a probe pulse is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed. The VUV radiation allowed us to observe the entire Franck-Condon envelope in photoionization from a transient electronic state, which was not possible in UV-DUV experiment in the laboratory.

並列關鍵字

He(I) ； photoelectron imaging

參考文獻

Chapter 1

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Eland, J. H. D. Photoelectron Spectroscopy, Butterworth, 1974.

Cooper, J.; Zare, R. N. J. Chem. Phys. 1968, 48, 942.

Samson, J. A. R.; Starace, A. J. Phys. B, At. Mol. Opt. Phys. 1975, 8, 1806.