Theoretical Studies On Low-energy Electron Collisions With Polyatomic Molecules

Electron-polyatomic molecule scattering dynamic process is very importance in astrophysics, plasmas physics, and radiation damages to biosystems. Firstly, in order to explore the dynamic mechanism of radiation damages to biomolecules, we have studied low-energy electron scattering with biomolecules using the quantum scattering method with the non-empirical model potentials in a symmetry-adapted, single-center expansion. The biomolecules studied in this thesis are DNA base tautomers, cyteine, cystine, and serine conformers. Secondly, due to thioformaldehyde and formamide play very important roles in astrophysics and photochemistry, low-energy electron collisions with thioformaldehyde and formamide have been studied using the R-matrix method.In the studies of shape resonance states of the low-energy electron attachments to DNA base tautomers, two different types of shape resonance, π*and σ*resonances, are found. Moreover, four and three π*resonances are predicted for purines and pyrimidines, respectively. Comparing the different tautomers of a certain DNA base, we found distinct differences both in the resonant energies and the resonant wave functions of π*shape resonances. In this work, we firstly explored and found tautomeric effects of DNA bases on shape resonances.Resonant dissociative electron attachments to cysteine and cystine have also been studied. In previous studies, an indirect dynamic mechanism for the specific bond cleavage is widely accepted. Meanwhile, previous works are mainly focused on one resonance. In this work, using one dimensional complex potential energy curves of the transient negative ion, we demonstrated another dynamic mechanism, i.e., a remarkable correlation between the different resonances and the specific bond cleavage. Furthermore, the wave function of the lowest shape resonance of temporary anion (cystine)-distinctly shows the localized anti-bond (S-S)*character, implying that this disulfide bond can be easily broken due to the low-energy electron resonant attachment.In the studies of low-energy electron scattering with serine conformers, on one hand, conformational effects of serine on shape resonances and dissociative dynamics via these resonances are found. On the other hand, a remarkable correlation between the different resonances and the specific bond cleavage are also found. Furthermore, the results calculated in this work are in good agreement with the recent experiment on dissociation electron attachment to serine.The elastic integral, differential, and momentum transfer cross sections and the excited cross sections for low-energy (0-10eV) electron collisions with thioformaldehyde molecule are calculated using the R-matrix method. Three core-excited shape resonances and three Feshbach resonances are determinded. The dissociative electron attachment processes at the first two core-excited shape resonances are proven by performing a series of scattering calculations, indicationg the S-(2P) yields together with the CH2fragment at three different states.Low-energy electron collisions with formamide have also been studied using the R-matrix method. The elastic integral cross section were calculated within static-exchange (SE), static-exchange-polarization (SEP), and close-coupling (CC) approximations. Moreover, A π*shape resonance was predicted at4.55,2.25and2.67eV within SE, SEP, and CC models, respectively. The position of the π*resonance is found to be sensitive to the treatment of polarization effects. The differential, momentum transfer, and excitation cross sections were also calculated in CC model. Besides the shape resonance, one core-excited shape resonance and three Feshbach resonances were predicted in CC model. These resonances calculated in this work could be responsible for the fragments observed in a recent experiment of the dissociation electron attachments to formamide.