| Abstract [eng] |
Ignas Gaižiūnas Modelling of Vibrational Modes of Ground and Excited Electronic States of Beta Carotene by Quantum Chemical Methods Summary Beta carotene belongs to a group of chemical compound called carotenoids. Carotenoids are organic pigments and are responsible for various important functions of living organisms. However, modelling of beta carotene is a time-consuming process that requires a lot of computational resources. For this reason, as well as to determine the influence of carbon rings and methyl radical groups on the vibrational and electronic spectra of beta carotene, beta carotene and simplified model molecules are modelled in this work. The aim of the study is to investigate the variation of the vibrational mode energies and vibrational forms of the lowest electronic states S0 and S2 of beta carotene and model molecules during electronic jumps and to determine the influence of the polyene chain and other beta carotene parts on these spectra. Analysis of geometry, electronic and vibrational spectra of beta carotene and model molecules in S0 and S2 states are performed in this work. In this work we also in more detail analyze the ν1 vibrational mode which is characteristic of carotenoids. All calculations are performed using DFT and TDDF methods at the B3LYP / 6-311g (d, p) theory level. The analysis of the state electronic spectrum and the geometric parameters of the polyene chain of the S0 and S2 states revealed similarities between investigated compounds. The geometrical changes in the polyene chain due to the simplifications of the introduced molecules were determined. Changes in the vibrational spectrum of the polyene chain in the S0 and S2 states were also evaluated. It has been found that the vibrational modes of a polyene chain in a particular electronic state should be expressed through a linear combination of several vibrational modes of another state. The contribution of anharmonism to the vibrational spectrum of the polyene chain was also evaluated in the course of the work. The influence of the last C = C bond from the carbon rings at the polyene chain and the methyl groups at the polyene chain on the electronic and vibrational spectrum was determined. |
