An Experimental Investigation On The Multiphoton Dissociation /Ionization Dynamics Of Methylamine And Carbon Tetrachloride

Atoms, molecules or radicals can be excited to a rovibrational state of the selected electronic state by the absorption of m-laser photons, and then the parent ion can be produced by absorption of another n-laser photons. Compared with the non-resonant absorption, the ion signal intensity can be increased drastically due to the resonant absorption between the intermediate states and the lower state. This multiphoton process is usually called Resonance Enhanced Multiphoton Ionization (REMPI). REMPI technique plays an important role in detecting the high excited electronic states of atoms, molecules and radicals. In particular, when the higher power laser is used as excited resource, we can detect high excited electronic states or Rydberg states of molecules and radicals with high signal-to-noise rate (SNR). Besides, we can select the special quantum states of molecules and radicals due to the high spectral resolution of the laser. Because of this, not only REMPI technique has been developed quickly, but also its application has been extensively enlarged. For example, it can be used to study the spectrum from high excited electronic states of molecules and radicals, photoionization and photodissociation dynamics, single atom detection, isotope separation, combustion diagnose and energy transfer between the electronical vibrational levels. No matter in basic or application research field, the study of REMPI and MPI of different systems has comprehensively scientific values and important background for future applications.Recently, the photodissociation of primary amines and halogen compounds have been attracted much attention because these species play a key role in atmospheric physics, environment pollution treatment, ecological preservation and society life. In this paper, the mechanism of multiphoton dissociation/ionization of primary amines and halogen compounds has been investigated by the REMPI-TOF technique. Some valuable conclusions are obtained from the analysis of the experiment results.In chapter one, the MPI technique and its development, background, character and applications are presented.In chapter two, the basic principles of MPI technique are introduced, which includes the selection rules of transition, REMPI rate equation and molecular Rydberg states etc.In chapter three, the setup of REMPI-TOF-MS and the experimental method are introduced.In chapter four, the multiphoton dissociation/ionization dynamics of methylamine is investigated in the range of 280-287.5nm. The main results are: (1) The TOF-MS and REMPI spectrum of methylamine are measured. (2) The TOF-MS of methylamine and the REMPI spectrum of the mass selected fragements and the parent molecule is analyzed. (3) The possible mechanism of dissociation/ionization is discussed. It is proposed that the main dissociation channel is the resonant photodissociation of the parent molecule firstly, followed by the photodissociation of the ionized fragment after the (1+1) multiphoton process.