Ionization Of Water Molecules Research Articles

Double ionization of water molecule induced by swift H+

SynopsisExperimental cross sections for single and double ionization of H2O by swift H+ with energy ranging from 0.5 to 2.0 MeV are reported. In this energy range the ionization is the dominant collision process and charge transfer reactions can be disregarded. A multi-hit coincidence technique was used to measure the H+ + OH+ and H+ + O+ fragmentation channels. A model calculation allowed us to separate the post collisional contribution from the direct double ionization process, whenever an electron vacancy occurs in the 2a1 molecular orbital.

140 Attacking mechanism of H and OH radicals to DNA base pair: DFT calculations in water

Genetic information recorded in DNA can be damaged indirectly by radiation. Such interaction of radiation to the water molecules in living organs produces the ionization of water molecules, leading...

H2Odouble ionization induced by electron impact

Double ionization of water molecules remains, still today, rarely investigated on both the experimental and the theoretical side. In this context, the present work reports on a quantum mechanical approach providing a quantitative description of the electron-induced double ionization process on isolated water molecules for impact energies ranging from the target ionization threshold up to about 10 keV. The cross section calculations are here performed within the first Born approximation framework in which the initial state of the system includes a molecular ground-state wave function expressed as a single-center linear combination of atomic orbitals while the final state of the system is characterized by two independent Coulomb wave functions used for describing the two ejected electrons coupled by a Gamov factor used for modeling the electron-electron repulsion. Besides, in order to go beyond the first Born approximation, the scattered electron is considered as a particle being in the Coulomb field of the nucleus---whose charge is screened by the ejected electrons---and then treated by an approximate Coulomb wave function. In this perturbative-type description, let us add that the passive (not ionized) electrons are considered as frozen in their molecular orbitals during the collision which permits to reduce the electron-target interaction potential to a two-active-electron problem. Comparisons with rare available experimental data are reported as well an energetic analysis in terms of mean secondary energy transfer during the double ionization process in order to demonstrate the relevance of the electron-induced double ionization process.

A hybrid distorted wave model: a (almost) complete-post version of the CDW model for single ionization

A hybrid CDW-CDW-EIS model is developed in order to include the dynamic screening in the post CDW approximation for single ionization. Doubly differential cross sections for single ionization of water molecules are calculated and comparison with available experimental data and other theories are shown.

Model potentials in liquid water ionization by fast electron impact

We study the ionization of water molecules in liquid phase by fast electron impact. We use our previous first-order model within an independent electron approximation that allows the reduction of the multielectronic problem into a monoelectronic one. The initial molecular states of the liquid water are represented in a realistic way through a Wannier orbital formalism. We complete our previous study by taking into account approximately the influence of the passive electrons of the target by means of different model potentials. We compute multiple differential cross sections for the most external orbital 1B1 and compare them with other results.

Proton-transfer mediated enhancement of nonlocal electronic relaxation processes in X-ray irradiated liquid water.

We have simulated the oxygen 1s Auger-electron spectra of normal and heavy liquid water using ab initio and quantum dynamical methods. The computed spectra are analyzed and compared to recently reported experimental data. The electronic relaxation in liquid water exposed to ionizing X-ray radiation is shown to be far more diverse and complex than anticipated and extremely different than for an isolated water molecule. A core-level ionized water molecule in the liquid phase, in addition to a local Auger process, relaxes through nonlocal energy and charge transfer, such as intermolecular Coulombic decay and electron-transfer mediated decay (ETMD). We evaluate the relative efficiencies for these three classes of relaxation processes. The quantitative estimates for the relative efficiencies of different electronic decay modes help determine yields of various reactive species produced by ionizing X-rays. The ETMD processes which are considered here for the first time in the core-level regime are found to have a surprisingly high efficiency. Importantly, we find that all nonlocal electronic relaxation processes are significantly enhanced by ultrafast proton transfer between the core-ionized water and neighboring molecules.

Leakage Current and Breakthrough Measurements on Moisturized SiCOH

At different moisture levels the leakage current and the disruptive strength of SiCOH, a nonporous low-κ dielectric, has been investigated. If water is in the dielectric film, the current density increased of about 6 orders of magnitude due to the ionization of water molecules in the applied electric field. Furthermore, at a constant electric field the delay time until the highest current value is reached depends on the water concentration and the silanol amount in the dielectric film. The delay time can vary between 1 minute in an untreated sample and 39 minutes in a thinner and plasma treated sample. In addition, the disruptive strength in the dry state and in the water saturated state at 80% relative humidity remains constant at about 10 MV/cm.

Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X̃(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B̃(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8].

Dynamics of low-energy electrons in liquid water with consideration of Coulomb interaction with positively charged water molecules induced by electron collision

To explain the electron energy relaxation process in water, we performed dynamical calculations of electrons in water using a simulation code developed in this study to calculate mean diffusion distances and mean energies of incident and secondary electrons released by the impact of the incident electron, as well as spatial probability-distribution of the secondary electrons. In addition to the following molecular processes of water: ionization: electronic, vibrational, and rotational excitation by electron impact; dissociative electron attachment; and elastic electron scattering, which were basic parameters used by Monte Carlo simulation, we newly took into account Coulomb interactions between electrons and positively ionized water molecules to calculate classical electron trajectories. We found that the Coulomb interactions enhance the number of collisions for the vibrational and rotational excitation processes at the incident 500eV electron energy. The secondary electrons diffuse to an average of 3nm from their original position, resulting much different spatial probability-distribution of those electrons in comparison to those previously reported. We also found that approximately 20% of the secondary electrons were returned to the parent ions within 100fs. By the electron re-capturing to either bonding or antibionding orbital, the molecules might be converted to some electronic excitation states. We suggest that the spatial probability-distribution of electrons, taken into account the re-capturing process, should be essential for detailed analysis of following chemical process arising in nanometer scales, such as biomolecular damage caused by radiation.

Electron DDCS in ionization of H2O by 72 MeV O8+ ions: comparison with CDW-EIS post and prior forms

We have measured energy and angular distributions of double differential cross-sections (DDCS) for electron emission in ionization of water molecule under the impact of 72-MeV O8+ ions. The DDCS values have been compared with a state-of-the-art CDW-EIS calculation for both the prior and post forms of scattering matrix. The prior form of the CDW-EIS model produces better quantitative agreement with the experimental data.

Influence of the description of the initial bound wavefunction in the single ionization reaction of H2O molecules

Single ionization of water molecules is considered. Influence of the description of the bound wave-function and of the continuum states is investigated.

Electron- and positron-induced ionization of water molecules: Theory versus experiment at the triply differential scale

Electron- and positron-induced ionization of water molecules: Theory versus experiment at the triply differential scale

Ionization of water molecules by ion beams. On the relevance of dynamic screening and the influence of the description of the initial state

Single ionization from water molecules by impact of protons, alpha particles and C6 + ions is studied. The post- and prior-versions of the continuum distorted wave-eikonal initial state (CDW-EIS) model within an independent electron approximation are employed to compute double differential cross sections. To avoid the complexity of using numerical molecular continuum states in the cross-section calculations, effective Coulombic continuum wavefunctions are employed. However, this may lead to the appearance of post–prior discrepancies and this fact is examined in detail. Moreover, the influence of the dynamic screening on this behaviour is studied. In addition, the contribution of different molecular orbitals to the angular spectrum is analysed for several ejection electron energies. Finally, the sensitivity of CDW-EIS calculations to the representation of the initial bound molecular orbitals is investigated.

The stereodynamics of the Penning ionization of water by metastable neon atoms

The stereodynamics of the Penning ionization of water molecules by collision with metastable neon atoms, occurring in the thermal energy range, is of great relevance for the understanding of fundamental aspects of the physical chemistry of water. This process has been studied by analyzing the energy spectrum of the emitted electrons previously obtained in our laboratory in a crossed beam experiment [B. G. Brunetti, P. Candori, D. Cappelletti, S. Falcinelli, F. Pirani, D. Stranges, and F. Vecchiocattivi, Chem. Phys. Lett. 539-540, 19 (2012)]. For the spectrum analysis, a novel semiclassical method is proposed, that assumes ionization events as mostly occurring in the vicinities of the collision turning points. The potential energy driving the system in the relevant configurations of the entrance and exit channels, used in the spectrum simulation, has been formulated by the use of a semiempirical method. The analysis puts clearly in evidence how different approaches of the metastable atom to the water molecule lead to ions in different electronic states. In particular, it provides the angular acceptance cones where the selectivity of the process leading to the specific formation of each one of the two energetically possible ionic product states of H2O(+) emerges. It is shown how the ground state ion is formed when neon metastable atoms approach water mainly perpendicularly to the molecular plane, while the first excited electronic state is formed when the approach occurs preferentially along the C2v axis, on the oxygen side. An explanation is proposed for the observed vibrational excitation of the product ions.

Double differential cross sections for ionization of water molecules by ion impact

Single ionization from water molecules by impact of bare ions is studied. Different approximations are employed, within the post and prior versions of the continuum distorted wave–eikonal initial state model, to calculate double differential cross sections. Post–prior discrepancies are observed between theoretical results. The sensitivity of the calculations to the description of the initial bound orbitals is investigated.

Proton Transfer in Nucleobases is Mediated by Water

Water plays a central role in chemistry and biology by mediating the interactions between molecules, altering energy levels of solvated species, modifying potential energy profiles along reaction coordinates, and facilitating efficient proton transport through ion channels and interfaces. This study investigates proton transfer in a model system comprising dry and microhydrated clusters of nucleobases. With mass spectrometry and tunable vacuum ultraviolet synchrotron radiation, we show that water shuts down ionization-induced proton transfer between nucleobases, which is very efficient in dry clusters. Instead, a new pathway opens up in which protonated nucleobases are generated by proton transfer from the ionized water molecule and elimination of a hydroxyl radical. Electronic structure calculations reveal that the shape of the potential energy profile along the proton transfer coordinate depends strongly on the character of the molecular orbital from which the electron is removed; i.e., the proton transfer from water to nucleobases is barrierless when an ionized state localized on water is accessed. The computed energetics of proton transfer is in excellent agreement with the experimental appearance energies. Possible adiabatic passage on the ground electronic state of the ionized system, though energetically accessible at lower energies, is not efficient. Thus, proton transfer is controlled electronically, by the character of the ionized state, rather than statistically, by simple energy considerations.

TH‐F‐105‐02: Molecular Dynamics Simulation of DNA Damage Induction by Ionizing Radiation

Purpose: To present a multi‐scale simulation of early stage of DNA damage by the indirect action of hydroxyl (OH) free‐radicals generated by electrons and protons in a real‐time animation and to present a comparison of the ratio of the total DNA double strand breaks induced by proton and electron tracks. Methods: The computational method comprises of interfacing Geant4‐DNA Monte Carlo (MC) with ReaxFF molecular dynamics (MD). A clustering method was employed to map the coordinates of OH‐radicals extracted from the ionization track‐structures simulated in 1 cm3 of continuous water onto 1019 of 2.6*2.6*6 nm3 simulation voxels (SV) filled with DNA and water molecules. The MD simulation sampled out of a large population of SVs provides the time evolution and chemical reactions and the energy‐landscape accounted for ensemble of DNAs surrounded by OH and water molecules. Such computational approach allows first principle enumeration of the DNA‐lesions induced by ionizing radiation. Results: We present cascade of chemical reactions between OH‐radicals and DNA induced by beam of electrons and protons. As a Result of ionization of water molecules in the surrounding environment MD simulation reveals broken bonds and identify chemical pathways for carbonyl‐and hydroxyl‐hole formation in the sugar‐moiety rings, nucleotide‐nucleotide hydrogen bond disruption, and nucleotide structural damage. We trace the dynamics of OH and demonstrate the interaction among them and DNA. We find 5% and 20% of the electron and proton track, respectively, populate SVs with at least one pair of ions, capable of forming DSBs. Taking into account the realistic ion distributions, we find that the ratio of the total DNA double strand breaks induced by a single proton and electron track is approximately 4. Conclusion: The first‐generation of hybrid MD‐MC method developed recently in our group allows comparison between the DNA damage induced by beams of electrons and protons.

Ionization of water molecules by proton impact: Two nonperturbative studies of the electron-emission spectra

Two nonperturbative methods are applied to obtain total and singly differential (in the electron energy) cross sections of electron emission in proton collisions with H${}_{2}$O at impact energies in the range 10 keV $\ensuremath{\le}{E}_{\mathrm{p}}\ensuremath{\le}$ 5 MeV. Both methods, one classical and one semiclassical, combine an independent particle treatment with a multicenter model potential description of the target. The excellent agreement obtained with experimental data supports the usefulness of the approximations involved and encourages the study of more complex systems.

Irradiation of the water molecule by the femtosecond laser field

By means of the time-dependent density functional theory (TDDFT) (applied to valence electrons), coupled with non-adiabatically molecular dynamics of ions, the excitation and dynamics of water molecules in a laser field with different polarizations have been explored. It is found that for the same polarization, the water molecule ionization can be enhanced with increasing laser intensity, while the laser intensity keeps constant, the ionization shows a maximum when the polarization is along the molecular symmetry axis, and the ionization is suppressed maximally when the polarization is perpendicular to the symmetry axis of the water molecule. The study of the dipole moment indicates that when the molecule is in the linear response region, there is only the oscillation of Dx for the case of the polarization along the x axis, while there is only the oscillation of Dy for the case of the polarization along the y axis. The bond lengths and the bond angle of H2O molecules are enlarged, while their may ictudes decrease with increasing polarization angle. Furthermore, it is found that in different polarization cases the vibration frequency of OH bonds is almost the same as the laser frequency during the action of the laser field, and it decreases after the laser pulse is switched off; however, the vibration mode of H2O molecule is sensitive to the laser polarization.

Growth of controllable ZnO film by atomic layer deposition technique via inductively coupled plasma treatment

An inductively coupled plasma technique (ICP), namely, remote-plasma treatment was introduced to ionize the water molecules as the precursor for the deposition of ZnO film via the atomic layer deposition processes. Compared with the H2O gas as the precursor for the ALD growth, the ionized water molecules can provide a lesser energy to uniformly stabilize oxidization processes, resulting in a better film quality with a higher resistivity owing to less formation of intrinsic defects at a lower growth temperature. The relationship between resistivity and formation mechanisms have been discussed and investigated through analyses of atomic force microscopy, photonluminescence, and absorption spectra, respectively. Findings indicate that the steric hindrance of the ligands plays an important rule for the ALD-ZnO film sample with the ICP treatment while the limited number of bonding sites will be dominant for the ALD-ZnO film without the ICP treatment owing to decreasing of the reactive sites via the ligand-exchange reaction during the dissociation process. Finally, the enhanced aspect-ratio into the anodic aluminum oxide with the better improved uniform coating of ZnO layer after the ICP treatment was demonstrated, providing an important information for a promising application in electronics based on ZnO ALD films.