Franck-Condon Analysis Study On The Photoelectron Spectra Of Some Small Negative Ions

The Franck-Condon analysis method is an efficient means to study and analyze molecular spectra. Quantitative applications of the Franck-Condon principle have become a very important means for people to understand matter structure laws,identify the electronic states involved in the transition and obtain spectroscopic constants. For the simple stable molecules, the molecular structure and vibrational frequency can be obtained directly from well-resolved spectral line positions. However, for complex or unstable molecules, spectroscopic techniques still suffer from some limitations. For instance, it is difficult to interpret electronic spectra with complicated overlapping vibrational structure. Nowadays, It has become a hot study how to obtain spectral parameters and molecular structures of the transient species from vibrational resolvable spectra. In this thesis, the studies on the calculations of Multidimensional Franck-Condon integrals,the method of Franck-Condon analysis and the application of iterative Franck-Condon analysis to simulate photoelectron spectra of some small negative ions hanve been present.This thesis is divided into four parts. In chapter one, the development of study for multidimensional Franck-Condon integrals and application of Franck-Condon analysis to spectral simulations are briefly introduced. In chapter two, the basic principle of the molecular orbits ab initio is presented. In chapter three, the method of Franck-Condon analysis used in our study has been introduced in detail, including the processing of mode mixing effect, the formulation for Franck-Condon factors, the iterative Franck-Condon analysis method, spectra simulations and the interface between spectra simulations and quantum chemistry calculation. In chapter four, the structure and photoelectron spectra of some radicals and its anions which play an important role in planetary atmospheres and other astrophysical environments have been theoretically analyzed. Firstly, geometry optimization and harmonic vibrational frequency calculations of small molecules S2 O,P2 H,PO 2 and its negative ions were performed by appling the method of quantum chemistry calculation at different levels with different basis sets. Secondly, based on the computed Franck-Condon factors (FCFs) and spectral simulations, the theoretical photoelectron spectra of these anions were obtained and the simulated spectra have been carefully analyzed. Under the Born-Oppenheimer and harmonic oscillator approximation, FCFs including the Duschinsky effect were calculated with the use of generation function method. Finally, the equilibrium geometry parameters of these negative ions S2 O?,P 2 H?,P O?2 were derived from employing an iterative Franck-Condon analysis procedure in the spectral simulations. In addition, through accuracy energy model, the calculated electron affinity of PO 2 was obtained as well.