A local collision probability approximation for predicting momentum transfer cross sections

The local collision probability approximation (LCPA) method is introduced to compute molecular momentum transfer cross sections for comparison to ion mobility experiments. The LCPA replaces the (non-local) scattering trajectory used in the trajectory method to describe the collision process by a (local) collision probability function. This momentum transfer probability is computed using the exact same analyte–buffer interaction potential as used in the trajectory method. Subsequently, the momentum transfer cross section Ω_LCPA(T) is calculated in a projection-type manner (corrected for shape effects through a shape factor). Benchmark calculations on a set of 208 carbon clusters with a range of molecular size and degree of concavity demonstrate that LCPA and trajectory calculations agree closely with one another. The results discussed here indicate that the LCPA is suitable to efficiently calculate momentum transfer cross sections for use in ion mobility spectrometry in conjunction with different buffer gases.