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Ab initio study of vibronic effects in molecules and chemical processes"


Author: Bălan Iolanta
Degree:doctor of chemistry
Speciality: 02.00.04 - Physical chemistry
Year:2019
Scientific adviser: Ivan Ogurţov
doctor habilitat, professor, Moldova State University
Scientific consultant: Natalia Gorincioi
doctor, associate professor (docent), Institute of Chemistry of the ASM
Institution: Moldova State University

Status

Term of presenting of the thesis 13 December, 2019

Abstract

Adobe PDF document0.93 Mb / in romanian

Thesis

CZU 544.222.3(043)

Adobe PDF document 3.19 Mb / in romanian
123 pages


Keywords

ab initio, quantum-chemical calculations, Jahn-Teller Effect (JTE), Pseudo Jahn-Teller Effect (PJTE), degeneration, pseudodegeneration, vibronic interaction, vibronic constants, Jahn-Teller stabilization energy

Summary

Thesis structure: The thesis consists of introduction, four chapters containing theoretical concepts and personal contributions of results obtained by ab initio calculations, general conclusions and recommendations, bibliography with 155 sources, 121 pages (106 pages of main text), 47 figures, 21 tables and 54 equations. The obtained results were published in 21 scientific publications (10 articles and 11 theses at international and national conferences).

The purpose of the thesis: the study of the electronic structure and the vibronic effects in different molecular systems and chemical processes on the base of ab initio calculations.

Objectives of the research: Study of electronic structure and unusual electrical properties of molecules with degenerate electronic states; Theoretical study of JT and PJT instability of nuclear configurations of molecules; Investigation of influence of the PJTE on the geometrical structure and proton transfer in protonated water clusters of different dimensions; Determination of structural changes for a number of molecular systems in the redox processes and by their coordination induced by changes of JTE and PJTE.

Scientific novelty and originality: For the first time, the values of multipol moments and polarizability for the Jahn-Teller systems (molecular systems with the degenerate electronic states) were calculated. For the first time, it was established that decomposition of the large protonated water clusters up to dihydronium cation and proton transfer in it are due to PJTE. It is shown that the structural changes of AH3 (A = N, C) and X2CE (X= H, F; E= O, S, Se) molecules in redox processes are caused by the changes of the PJTE.

The solved important scientific problem: is to identify the vibronic origin of structural instability of high-symmetry nuclear configurations of considered molecular systems on the basis of ab initio calculations and the vibronic effects (JT and PJT).

Theoretical significance: The thesis contributes to the understanding of the origin of the instability of the geometry of free and coordinated molecular systems in their neutral and ionized states. Demonstration of the increase or suppression of EJT and PEJT in redox processes provides a "tool" for manipulating the molecular structure.

The applicative value of the present work is the possibility of using the developed procedures for the investigation of other molecular systems and chemical processes (redox, adsorption, coordination, catalytic, etc.), in which the stability or instability of the nuclear configuration play a significant role.

The elaborated theoretical study can be applied in various scientific fields to complete and explain the experimental results and offers the possibility to obtain substances with desired structures and properties.

The theoretical results of the vibronic effects in molecules and chemical processes published by us are cited in the scientific literature.

Implementation of scientific results. A series of results serve as a teaching material in the "Computational Chemistry" course at the Department of Chemistry of the Moldova State University.