分子束多原子分子之紫外光光電子影像

Abstract

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.

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.