Theoretical investigations of collision dynamics of cytosine by low-energy (150-1000 eV) proton impact

Using a real-space real-time implementation of time-dependent density functional theory coupled to molecular dynamics（TDDFT-MD） nonadiabatically,we theoretically study both static properties and collision process of cytosine by150-1000 eV proton impact in the microscopic way.The calculated ground state of cytosine accords well with experiments.It is found that proton is scattered in any case in the present study.The bond break of cytosine occurs when the energy loss of proton is larger than 22 eV and the main dissociation pathway of cytosine is the breaks of C1 N2 and N8 H10.In the range of 150 eV≤Ek≤360 eV,when the incident energy of proton increases,the excitation becomes more violent even though the interaction time is shortened.While in the range of 360 eV<Ek≤1000 eV,the excitation becomes less violent as the incident energy of proton increases,indicating that the interaction time dominates mainly.We also show two typical collision reaction channels by analyzing the molecular ionization,the electronic density evolution,the energy loss of proton,the vibration frequency and the scattering pattern detailedly.The result shows that the loss of electrons can decrease the bond lengths of C3 NS and CSN6 while increase the bond lengths of C4 H11,C5 H12 and C4 C5 after the collision.Furthermore,it is found that the peak of the scattering angle shows a little redshift when compared to that of the loss of kinetic energy of proton.

Collision site effect on the radiation dynamics of cytosine induced by proton

By combing the time-dependent density functional calculations for electrons with molecular dynamics simulations for ions(TDDFT-MD)nonadiabatically in real time,we investigate the microscopic mechanism of collisions between cytosine and low-energy protons with incident energy ranging from 150 e V to 1000 e V.To explore the effects of the collision site and the proton incident energy on irradiation processes of cytosine,two collision sites are specially considered,which are N and O both acting as the proton receptors when forming hydrogen bonds with guanine.Not only the energy loss and the scattering angle of the projectile but also the electronic and ionic degrees of freedom of the target are identified.It is found that the energy loss of proton increases linearly with the increase of the incident energy in both situations,which are14.2%and 21.1%of the incident energy respectively.However,the scattering angles show different behaviors in these two situations when the incident kinetic energy increases.When proton collides with O,the scattering angle of proton is larger and the energy lost is more,while proton captures less electrons from O.The calculated fragment mass distribution shows the high counts of the fragment mass of 1,implying the production of H+fragment ion from cytosine even for proton with the incident energy lower than keV.Furthermore,the calculated results show that N on cytosine is easier to be combined with low-energy protons to form NH bonds than O.