Classical Trajectories and RRKM Modeling of Collisional Excitation and Dissociation of Benzylammonium and tert Butyl Benzylammonium Ions in a Quadrupole-Hexapole-Quadrupole Tandem Mass Spectrometer
Vadim D. Knyazev, Stephen Stein
Collision-induced dissociation of the benzylammonium and the 4-tert butyl benzylammonium ions was studied experimentally in an electrospray ionization quadrupole-hexapole-quadrupole tandem mass spectrometer. Ion fragmentation efficiencies were determined as functions of the kinetic energy of ions and the collider gas (argon) pressure. A theoretical Monte Carlo model of ion collisional excitation, scattering, and decomposition was developed. The model includes simulation of the trajectories of the parent and the product ions flight through the hexapole collision cell, quasiclassical trajectory modeling of collisional activation and scattering of ions, and RRKM modeling of the parent ion decomposition. The results of modeling demonstrate that quasiclassical trajectory calculations using physically realistic soft interatomic potential do not provide sufficient activation of ions to account for the observed experimental fragmentation efficiencies. However, use a of hard-spheres interatomic potential with a collision efficiency factor of 2/3 results in general agreement between calculations and experiment. Calculated values of ion fragmentation efficiency are sensitive to scattering of product ions from the collision cell and to the distribution of initial ion velocities orthogonal to the axis of the collision cell. Two critical parameters of the model were adjusted to reproduce the experimental data on the dissociation of the benzylammonium ion; application of the model without any further adjustments to decomposition of the t butyl benzylammonium ion results in general agreement with the experimental data, except for the conditions of largest pressures and moderate (3 5 eV) ion kinetic energies. Energy distribution functions obtained in modeling depend on the average numbers of collisions between the ion and the atoms of the collider gas and, in general, have non-Boltzmann shapes.
Journal of the American Society for Mass Spectrometry
and Stein, S.
Classical Trajectories and RRKM Modeling of Collisional Excitation and Dissociation of Benzylammonium and tert Butyl Benzylammonium Ions in a Quadrupole-Hexapole-Quadrupole Tandem Mass Spectrometer, Journal of the American Society for Mass Spectrometry
(Accessed November 30, 2023)