Structure of the cluster ions of ketones in the gas phase according to ion mobility spectrometry and ab initio calculations

Ion mobility spectra were recorded for linear aliphatic ketones with three to nine carbon atoms. Two most intense peaks were found to be the peaks of the monomer and dimer and used to calculate the reduced ion mobilities and the scattering (collision) cross sections (by the Mason-Schamp equation). The scattering cross sections increased linearly with the molecular mass. Based on the results of experiments and quantum-chemical calculations, it was concluded that the formation of the acetone dimer is accompanied by a decrease in the dipole moment of the structure relative to that of the monomer. For higher ketones, there is no compensation of the dipole moment.