Theoretical Mass Spectra of PE, PP, PS and PET Polymers by QMD Methods Using the Model Molecules

Abstract

We used a quantum molecular dynamics {QMD (MD with MO)} due to the force function of MO with the velocity Verlet algorithm using the model oligomers of PE, PP, PS, and PET polymers to obtain theoretical mass spectra of the polymers. The QMD calculation was performed in the thermal energy range of 0.69 - 0.95 eV, and the sampling position data by a time step of 0.5 fs were performed up to 5000 steps. The fragments at the final step of 60 trajectories in the QMD were obtained as positive, negative, and neutral charged ones from the net atomic charge analysis at geometry-optimization of the MO SCF calculations. We can compare the positive ion fragments of polymer models with the experimental distribution of polymers in mass spectra and secondary ionization mass spectra after a few tens of keV of primary heavy metal ion bombardment. We also showed the chemical structures of fragments for PE, PP, PS, and PET polymers in positive ion spectra, unavailable from experimental methods.