Theoretical Studies On Vibrational And Rotational Spectra And Dissociation Energies Of Diatomic Molecules

There are two parts in this dissertation. An algebraic method (AM) is proposed to study the full vibrational energy spectrum of a stable diatomic molecular system, and a potential variational method (PVM) is proposed to study the rotational spectrum and vibrational force constants in part one. A dissociation limit method (DLM) is proposed to study molecular dissociation energies for diatomic molecules in part two.In the first part, the AM is used to obtain accurate full vibrational spectrum {Ev} from limited known accurate vibrational energies in a subset [Ev] for more than two dozen electronic states of diatomic molecules. It is shown that: (1) the so obtained AM full vibrational spectrum {Ev} is accurate, and the accuracy is the same as that of the input subset [Ev}; (2) the AM makes it possible to have highly excited accurate vibrational energies for a lot of diatomic electronic states which are used in many researches such as molecular structure and spectrum, chemical reaction, and molecular scattering, etc.Based on the AM vibraational spectrum constants, the PVM is used to obtain correct vibrational force constants fn (n=2~8) and rotational spectrum constants for diatomic systems.The second part studies the molecular dissociation energies De for some diatomic electronic states using the proposed DLM. The results indicate that the DLM not only can obtain correct dissociation energies within satisfied accuracy which may be difficult to have experimentally, but also can judge the physical qualities of different sets of vibrational spectrum constants from different studies for same molecular electronic state.