Aspectos da natureza da geometria molecular de hidretos DI-E triatomicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1988

RESUMO

Two words may represent the character of this thesis: MOLECULAR GEOMETRY. The main objective is to analyse the nature of molecular geometry in some di and triatomic hydrides. Methods of empirical, semi-empirical and "ab inito" nature were employed. The thesis is divided in six(6) chapters due to the nature of the methods employed and the analytical scheme used. Basically, we employ the method of Mulliken population analysis and a method of partitioning energies within the Born-Oppenheimer approximation. The main conclusions obtained are: a) It is not possible to calculate the correct molecular geometry without hybridization. The maximum overlap criterion can not be considered to be responsible for the determination of the geometry; b) For triatomic hydrides, the electronic repulsion is considered to be respossiblçe for the molecular geometry. The partitioning of this energy produces some results that are in agreement with some rules of the "valence shell electron pair repulsion" (VSEPR) model; c) With a modification of koopmans theorem by imposition of the virial theorem, the ionization energy can be expressed as a sum of three terms, the orbital kinetic energy term, the kinetic relaxation term and work term. The first term provides information about diffuseness of the orbital, the secondterm the relaxation effect of the electronic cloud upon ionization, and the third term about bonding, non-bonding and anti-bonding character of the molecular orbital. This information complements some aspects of the Mulliken and Walsh correlation digrams; d) Partition of the kinetics and nuclear attraction energies is possible in the CNDO/2 method and results obtained are qualitatively similar to those obtained by "ab initio" calculations if basics functions in the CNDO/2 are orthogonalized and the scaling method of lowdin in not employed to force the obedience of the virial theorem; e) Ionization energies and partitions of these energies obtained by the correction introduced by the virial theorem on the koopamans theorem shows that the orthogonalized data using the Schmidt/Lowdin method in CNDO/2 are closer to the "ab initio" ones, and f) point charge models may produce information on the nature of molecular geometry, and some information is similar to those obtained by "ab initio" calculations.

ASSUNTO(S)

hidretos estrutura molecular orbitais moleculares

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