The Metal Atom Beam Source Developed And Li And Co Fast Electron Energy Loss Spectroscopy

In the present work,a resistively heated atomic beam source has been developed to provide vapor target for the fast electron energy loss spectrometer.A data acquisition system for the same spectrometer has been developed,where the multithreading technology is used to improve the accommodating-err ability.Two optically forbidden autoionizing states of(1s2s~2) ~2S and (1s2s ~3S)3s ~2S were observed in the electron energy loss spectra of lithium,and the momentum transfer dependence behaviors of the generalized oscillator strength ratios for 1s(2s2p ~3P)~2P~0 to 1s(2s2p ~1P)~2P~0 were investigated.The relative intensity distributions and generalized oscillator strengths for the valence shell vibronic bands of carbon monoxide were also determined.Then the momentum transfer dependence behaviors of Franck-Condon factors for these vibronic bands were investigated,and the optical oscillator strengths,as well as the integral cross sections of these transitions,were determined.All the present results were compared with the previous ones.In chapter 1,the method of angle-resolved fast-electron-energy-loss spectroscopy were described. Then the basic conception of the optical and generalized oscillator strengths,the differential and integral cross section,as well as the elements for the measurements of the generalized oscillator strengths utilizing electron energy loss spectrometer,were introduced.In addition,the gas mixture method of measuring the generalized oscillator strengths were introduced.In chapter 2,A resistively heated atomic beam source has been developed to provide vapor target of the alkali and alkaline-earth metals.The operating temperature of the oven is as high as 719℃,and the target intensity is enough high for the investigation of the autoionizing states.The contamination of the vacuum system and electron optical system by metal vapor deposition has also been minimized by a black body trap,whose collection efficiency is more than 90%.So the beam source can work continually for more than one month without cleaning.The heat transfer to vacuum chamber,as well as electric and magnetic fields created by the heating currents,were minimized by some special design.In chapter 3,the new data acquisition system for the one dimensional multichannel fast electron energy loss spectrometer,which can work in scan acquisition mode and static acquisition mode,was described.The timing precision of the scan mode is less than 4μs by utilizing the gated signal generated by data acquisition card DAQ2010 and an AND logic circuit.A timer card PCI8554 was used to synchronize the data acquisition card and the personal computer.The scan voltage supply was controlled by the personal computer through the RS232 interface.The multi-threading technology was used in the acquisition software in order to improve the accommodatingerr ability of the acquisition system. In chapter 4,the electron energy loss spectra for the inner shell excitations of atomic lithium were measured at an incident electron energy of 2500 eV and scattering angles of 0°,2°,4°and 6°.Two optically forbidden transitions of(1s2s~2) ~2S and(1s2s ~3S)3s ~2S were observed.The generalized oscillator strength ratios for 1s(2s2p ~3P)~2P~0 to 1s(2s2p ~1P) ~2P~0 were determined, and they are independent of the momentum transfer.The phenomena was elucidated based on the framework of the intermediate coupling.In chapter 5,the relative intensity distributions and generalized oscillator strengths for the vibronic bands of A~1Π,D~1Δ,B~1Σ~+,C~1Σ~+ and E~1Πof carbon monoxide were determined by an angle-resolved electron energy loss spectroscopy at an incident electron energy of 2500 eV and in an angular range of 0°-7°.The momentum transfer dependence behaviors of Franck-Condon factors for the vibronic bands of A~1Π,B~1Σ~+,C~1Σ~+ and E~1Πwere investigated.For the fist time, generalized oscillator strengths for v=9-11 of A~1Πand v=9-25 of D~1Δwere reported and the contribution from D~1Δwere taken into account when determining the relative intensities and generalized oscillator strengths for other transitions.The optical oscillator strengths,as well as the integral cross sections,of the vibronic bands of A~1Π,B~1Σ~+,C~1Σ~+ and E~1Πwere determined from the generalized oscillator strength data.The present experimental results were compared with previous works,and some differences between them have been explained.