Classical trajectories and RRKM modeling of collisional excitation and dissociation of benzylammonium and <Emphasis Type="Italic">tert</Emphasis>-butyl benzylammonium ions in a quadrupole-hexapole-quadrupole tandem mass spectrometer |
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Authors: | Vadim D Knyazev Stephen E Stein |
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Institution: | 1.National Institute of Standards and Technology,Physical and Chemical Properties Division,Gaithersburg,USA;2.Research Center for Chemical Kinetics, Department of Chemistry,The Catholic University of America,Washington,USA |
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Abstract: | 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 Rice-Ramsperger-Kassel-Marcus
(RRKM) modeling of the parent ion decomposition. The results of modeling demonstrate a general agreement between calculations
and experiment. Calculated values of ion fragmentation efficiency are sensitive to initial vibrational excitation of ions,
scattering of product ions from the collision cell, and distribution of initial ion velocities orthogonal to the axis of the
collision cell. Three critical parameters of the model were adjusted to reproduce the experimental data on the dissociation
of the benzylammonium ion: reaction enthalpy and initial internal and translational temperatures of the ions. Subsequent application
of the model to decomposition of the t-butyl benzylammonium ion required adjustment of the internal ion temperature only. 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. |
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Keywords: | |
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