Numerical modelling of the temperature dependence of NQR transition frequencies in molecular crystals

Paul Josef Krassnig

Research output: ThesisMaster's Thesis


In the course of the FET-Open project “CONQUER”, Bi-aryl compounds proved to be promising in terms of their physical and chemical properties to enable quadrupole relaxation enhancement. Knowledge of Bi-aryl compound’s temperature sensitivity is of great importance to predict the desired frequency crossing of NQR transition frequencies and the Larmor frequency of protons at certain field strength more precisely. The aim of this master’s thesis is to model the temperature dependence of NQR transition frequencies of Triphenylbismuth and Tris(2methoxyphenyl)bismuthine based on molecular motions, precisely torsional oscillations. The focus is set on numerical modelling to overcome commonly applied assumptions and approximations, which are constant asymmetry parameter of the electric field gradient and small angle approximation of torsional oscillations, used by analytical models. Their influence on modeled NQR transition frequencies as well as benefits of numerical implementations are displayed and analyzed. Furthermore, a novel numerical fitting approach, involving two NQR transition frequencies at once (increased data set for fitting), is presented. Obtained fitting parameters of Triphenylbismuth, such as torsional frequency and equivalent moment of inertia, of analytical and numerical models are comparable and have plausible orders of magnitude. Generally, Triphenylbismuth shows a greater response to temperature than Tris(2-methoxyphenyl)bismuthine. Interestingly, numerical simulations of different torsional oscillation directions revealed to have an impact on the sign of the temperature coefficient of the lowest transition in case of an axially asymmetric electric field gradient. Finally, important aspects and improvements concerning future modelling processes of the temperature dependence of NQR transition frequencies are proposed.
Original languageEnglish
QualificationMaster of Science
Awarding Institution
  • Graz University of Technology (90000)
  • Scharfetter, Hermann, Supervisor
  • Gösweiner, Christian, Supervisor
Publication statusPublished - 2019

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