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Vibracijska dinamika molekula s unutrašnjom rotacijom na niskim temperaturama

Mohaček Grošev, Vlasta (1995) Vibracijska dinamika molekula s unutrašnjom rotacijom na niskim temperaturama. Doctoral thesis, Sveučilište u Zagrebu, Prirodoslovno-matematički fakultet.

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Molecules exhibiting internal rotation represent a fundamental problem as well as a model for analysis of the dynamics of biologically interesting molecules, where the appearance of hydrogen bonds and ring-puckering makes the vibrational problem even more complicated. By choosing the nitromethane and toluene molecules which have methyl group (which is a symmetric top) and whose internal rotation transitions can be observed in low-frequency Raman spectra we have made the first necessary step towards better understanding of the more complicated situations where the asymmetric rotors perform large amplitude motions. Raman spectroscopy is a good method for investigating the barrier height of a rotor in molecular crystal. If one chooses a proper band that is sensitive to the movement of some specific group of atoms and measures its bandwidth as a function of temperature, one can acquire and estimate of the barrier height for the rotation of that particular atomic group in the molecule. For nitromethane the barrier for the internal rotation of methyl group was found to be 193 plus/minus 6 cm-1 , approximately 80 cm-1 less than accepted value found in the literature. It has also been shown that Raman spectroscopy can be used to detect any possible mesophase into which a molecular crystal may change when heated, even if the temperature interval is as narrow as 2 K. In the case of nitromethane two plastic phases were detected in 237 K - 240 K interval below the melting point (241 K by Raman spectroscopy). In the case of toluene one plastic phase was found at 167 K.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: internal rotation; Raman spectroscopy; Mathieu equation; lattice dynamics; nitromethane; toluene; methyl group; cryostat
Subjects: NATURAL SCIENCES > Physics > Atomic and Molecular Physics
Divisions: Division of Materials Physics
Depositing User: Vlasta Mohaček Grošev
Date Deposited: 19 Jul 2022 07:43

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