posted on 2016-01-25, 00:00authored byLiene I. De Beuckeleer, Wouter A. Herrebout
Acetone
molecules are inclined to self-associate through dipole–dipole
interactions because of their large dipole moment. Infrared spectroscopy
of compounds dissolved in liquid noble gases supported by high level ab initio calculations allows investigating the self-associating
behavior and determining the thermodynamical properties. In this study,
infrared spectra of various concentrations of acetone dissolved in
liquid krypton are recorded at constant temperature. Overlapping monomer
and dimer spectra are separated by analyzing the obtained data sets
with numerical methods based on least-squares fitting. Although acetone
is known to self-associate, only a few spectral features have been
presented in literature before. In this study, the application of
new numerical approaches succeeds in resolving overlapping spectra
and allows observing isolated acetone dimer absorption bands for the
complete mid infrared spectrum. By use of data sets of spectra recorded
at temperatures between 134 and 142 K, the experimental standard dimerization
enthalpy was determined to be −10.8 kJ mol–1. MP2/aug-cc-pVDZ calculations predicted a stacked and planar dimer
geometry of which the stacked geometry is more stable. Combining MP2
energies and single point corrections involving CCSD(T) calculations
and complete basis set extrapolations based on the MP2/aug-cc-pVDZ
equilibrium geometry lead to complexation energy of −28.4 kJ
mol–1 for the stacked geometry and −15.1
kJ mol–1 for the planar geometry. The corresponding
values for the complexation enthalpies in solution, obtained by combining
these values with corrections for thermal and solvent influences are
−13.7 and −5.8 kJ mol–1.