Untersuchungen zum Einfluss von London-Dispersionswechselwirkungen auf die Molekülaggregation

Influence of London dispersion on molecular aggregation

by Jonas Altnöder
Doctoral thesis
Date of Examination:2015-05-21
Date of issue:2015-06-24
Advisor:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Martin A. Suhm
Referee:PD Dr. Thomas Zeuch
Persistent Address: http://dx.doi.org/10.53846/goediss-5130

 

 

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Abstract

English

The energetics and dynamics of intermolecular interactions are at the core of fundamental research in physical chemistry. Noncovalent intermolecular interactions are studied on all scales of molecular size, ranging from dimers of noble gas atoms and small water aggregates up to synthetic polymers, peptides, and DNA. This work focusses on small aggregates from dimers to tetramers. They are prepared in supersonic free-jet expansions and studied by vibrational spectroscopy, namely FTIR absorption and Raman scattering. The hydrogen-bonded dimers of glycolaldehyde, 1-indanol, 2-methyl-1-propanol, cyclohexylmethanol, and benzyl alcohol are studied in the OH stretching range. These studies profit from the characteristic wavenumber shifts and gains in infrared band strength which hydrogen bonding induces on the donor OH stretching vibration. Weak hydrogen bonds and stacking interactions of methylated amides (N,N-dimethyl formamide and N,N-dimethyl formanilide) are studied in the carbonyl and fingerprint region. All experimental jet spectra are compared to energy and wavenumber predictions of detailed quantum chemical calculations. The applied approximations include various dispersion-corrected density functional methods at GGA, hybrid, and double-hybrid level as well as correlated ab initio methods involving MP2 geometry optimizations and coupled cluster single point calculations with triple-zeta basis sets. The influence of London-dispersion interactions upon aggregation is qualitatively analyzed in terms of dispersion contributions of the Grimme D3 dispersion correction. Additionally, preparatory work on a modified FTIR jet experimental setup is discussed, which is intended to rely on infrared laser induced vaporization of nonvolatile organic substances prepared on single spheres of molecular sieve.
Keywords: hydrogen bonding; vibrational spectroscopy; supersonic jet; aggregation; quantum chemical calculations; dispersion-corrected DFT; FTIR; Raman
 
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