Experimental Study Of Photoionization Of The Excited States Of Metals

The photoionization cross section of an excited atom refers to the probability of an electron being emitted from its electronic state while atoms and photons interact with each other. Study the photoionization cross section could reveal the electronic structure, radiation recombination, multichannel ionization, multichannel interference, and so on. PCSs have widespread applications in many scientific fields, such as controlled thermonuclear research (CTR) plasmas, atmospheric physics, astrophysics, space science, radiation chemistry, physics and biology,and especially in the astrophysics it presents its importance. In addition, the accurate absolute photoionization cross sections also can test the theoretical calculation and promote the development of the theoretical model for the calculation of the PCSs.In this thesis, we have studied the absolute photoionization cross sections of the excited states of Fe, Co and Ti atoms. In the experiment, the free atoms were produced by using laser ablation of a metal sample and the ions are detected using the time of flight mass spectrometer. Scanning laser wavelength in the range of 298-351 nm, we obtained the REMPI spectra of the excited atoms by using Resonance-enhanced multiphoton ionization. And the photoionization cross sections were deduced from the dependence of the ion signal intensity on the laser intensity for photon energies close to the ionization threshold. This paper includes four chapters:In the first chapter, the research background and development on the photoionization cross section were summarized.In the second chapter, we introduce some related experimental techniques and including laser ablation, supersonic jet, time of flight mass spectrometry, the resonance-enhanced multi-ionization (REMPI).In the third chapter, the experiment setup and process were introduced. (The experiment setup mainly contains vacuum systems, molecular beam source system, laser system, timing control system and signal detection and acquisition system.)Chapter Four, We report the resonance enhanced multiphoton ionization (REMPI) spectra of the iron atoms, cobalt atoms and titanium atoms and the absolute photoionization cross sections (PCSs) of the several excited states of Fe I, Co I and Ti I in the range of 298-351 nm.