TY - BOOK

T1 - Stability and Isotopic Effects of OH-Bound Ether and Amine Complexes

AU - Kjærsgaard, Alexander

PY - 2020

Y1 - 2020

N2 - This thesis considers the formation of hydrogen and deuterium bound bimolecular complexes in the gas phase at room temperature using Fourier transform infrared spectroscopy. These complexes consist of a non- or singly deuterated alcohol or water donor molecule and an ether, amine or nitrile acceptor molecule. For all complexes, a vibrational band from the fundamental OH- or OD-stretch is observed that is redshifted relative to the fundamental OH- or OD-stretching band of the donor molecule. In spectra of complexes with a water donor, additional bands beside the hydrogen bound OH-stretch arise from the non-hydrogen bound OH-stretch, the HOH bending overtone and combinations bands of the OH-stretches and HOH bending modes. Transition wavenumbers and intensities of the bands of these complexes were computed using anharmonic local mode theory, based on either perturbative or variational approaches. This combination of experimental and calculated intensity allow accurate determination of the Gibbs energy of complex formation, with combined experimental and calculated errors of less than 1.0 kJ/mol. The work are presented in three topics. The first topic compares the relative stability of similar hydrogen and deuterium bound complexes, with a non- or singly deuterated methanol or ethanol donor and an ether and amine acceptor. At room temperature similar Gibbs energies of complex formation were observed for the corresponding hydrogen and deuterium bound complexes, in contrast to observations at cold conditions (~20 K) where the formation of the deuterated complex is heavily favored. The change in relative stability with respect to temperature for these complexes is explained by density functional theory calculations. The calculations show a lower complexation entropy for the deuterium bound complex relative to the hydrogen bound complex, favoring of the hydrogen bound complex as the temperature increases. In addition, for both of the methanol and ethanol donors used here, the entropic penalty of the deuterated complex arise predominantly from changes in both their vibrational and rotational entropy contributions. In the second topic, spectra of complexes with an acetonitrile acceptor are compared to spectra of complexes with a pyridine and trimethylamine acceptor. These complexes represent the nitrogen acceptor atom in the sp, sp2 and sp3 hybridization state for the acetonitrile, pyridine and trimethylamine acceptor molecules, respectively. The hybridization of the nitrogen acceptor atom is seen to significantly alter the strength of the complex, showing smaller complexation redshifts and higher Gibbs energies with decreasing s-character (sp<sp2 <sp3). The third topic investigate stabilities of bimolecular hydrated amine complexes. Five vibrational bands belonging to the complex were observed, and similar values of the complexation Gibbs energy were determined from each band. The similar values in the multiple determinations increase both the validity and versatility of our combined theoretical and experimental approach. The determination of complexation Gibbs energies of hydrated complexes have important implications in the formation of atmospheric areosol. Accurate values of the complexation Gibbs energy are important to benchmark theoretical approaches, as calculations of Gibbs energies can vary significantly using different ab initio methodologies.

AB - This thesis considers the formation of hydrogen and deuterium bound bimolecular complexes in the gas phase at room temperature using Fourier transform infrared spectroscopy. These complexes consist of a non- or singly deuterated alcohol or water donor molecule and an ether, amine or nitrile acceptor molecule. For all complexes, a vibrational band from the fundamental OH- or OD-stretch is observed that is redshifted relative to the fundamental OH- or OD-stretching band of the donor molecule. In spectra of complexes with a water donor, additional bands beside the hydrogen bound OH-stretch arise from the non-hydrogen bound OH-stretch, the HOH bending overtone and combinations bands of the OH-stretches and HOH bending modes. Transition wavenumbers and intensities of the bands of these complexes were computed using anharmonic local mode theory, based on either perturbative or variational approaches. This combination of experimental and calculated intensity allow accurate determination of the Gibbs energy of complex formation, with combined experimental and calculated errors of less than 1.0 kJ/mol. The work are presented in three topics. The first topic compares the relative stability of similar hydrogen and deuterium bound complexes, with a non- or singly deuterated methanol or ethanol donor and an ether and amine acceptor. At room temperature similar Gibbs energies of complex formation were observed for the corresponding hydrogen and deuterium bound complexes, in contrast to observations at cold conditions (~20 K) where the formation of the deuterated complex is heavily favored. The change in relative stability with respect to temperature for these complexes is explained by density functional theory calculations. The calculations show a lower complexation entropy for the deuterium bound complex relative to the hydrogen bound complex, favoring of the hydrogen bound complex as the temperature increases. In addition, for both of the methanol and ethanol donors used here, the entropic penalty of the deuterated complex arise predominantly from changes in both their vibrational and rotational entropy contributions. In the second topic, spectra of complexes with an acetonitrile acceptor are compared to spectra of complexes with a pyridine and trimethylamine acceptor. These complexes represent the nitrogen acceptor atom in the sp, sp2 and sp3 hybridization state for the acetonitrile, pyridine and trimethylamine acceptor molecules, respectively. The hybridization of the nitrogen acceptor atom is seen to significantly alter the strength of the complex, showing smaller complexation redshifts and higher Gibbs energies with decreasing s-character (sp<sp2 <sp3). The third topic investigate stabilities of bimolecular hydrated amine complexes. Five vibrational bands belonging to the complex were observed, and similar values of the complexation Gibbs energy were determined from each band. The similar values in the multiple determinations increase both the validity and versatility of our combined theoretical and experimental approach. The determination of complexation Gibbs energies of hydrated complexes have important implications in the formation of atmospheric areosol. Accurate values of the complexation Gibbs energy are important to benchmark theoretical approaches, as calculations of Gibbs energies can vary significantly using different ab initio methodologies.

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/1pioq0f/alma99123849765705763

M3 - Ph.D. thesis

BT - Stability and Isotopic Effects of OH-Bound Ether and Amine Complexes

PB - Department of Chemistry, Faculty of Science, University of Copenhagen

ER -