Fragment Distribution of Polystyrene by QMD Method Using the Model Hexamer

Abstract

A quantum molecular dynamics (QMD) due to the force function of MO with the velocity Verlet algorithm using the polystyrene (PS) hexamer was performed to simulate secondary ion mass spectra (SIMS) of the polymer. We assumed that the QMD calculation corresponds to the thermal sputtering process in Sigmund proposal, and tried to analyze experimental mass spectra of PS with size-selected Ar gas cluster ion beam (GCIB) bombardments from the calculated mass spectra, because the Ar GCIB bombardments are considered as the sputtering by elastic collisions proposed by Sigmund. The calculated positive ion mass spectra for PS 6mer from the atomic charge analysis of the fragments at the 5000 MD (2.5 ps) step for total 60 trajectories of 0.77, 0.86 and 0.95 eV energy controls seem to be roughly in accordance with the experimental secondary positive ion results with the Ar⁺ primary ion bombardments. From analysis of energy-dependency (0.43 - 1.03 eV) for the PS model in QMD, the calculated relative intensities of fragments (C₂H₂⁺, C₃H₄⁺, C₄H₂⁺, C₆H₄⁺, C₈H₇⁺, C₉H₉⁺) may almost correspond to the experimental E_atom dependence of relative yields of fragments (C₂H₃⁺, C₃H₃⁺, C₄H₃⁺, C₆H₅⁺, C₈H₇⁺, C₉H₇⁺)