Investigation of ion–molecule collisions with laser-based ion mobility spectrometry

A home-built laser-based ion mobility (IM) spectrometer was employed for the investigation of 19 aromatic compounds ranging from benzene to C60 fullerene. With N2 as drift gas, the reduced mobilities K0 obtained range from (2.51 ± 0.03) for benz+ to (1.02 ± 0.05) × 10−4 m2 V−1 s−1 for C60+. The resolution of the IM apparatus, defined as the ratio of the drift time and the peak temporal width, was typically R = 20–50 which could be improved to R = 75 under optimal experimental conditions. A suitable mass-mobility correlation within the hard sphere (HS) approximation was obtained under the assumption that the radii of the aromatic ions vary with the cubic root of the ionic masses. Several parameters, such as diffusion coefficients, ionic radii and collision rate constants, were derived from the mobility measurements.